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/************************************************************* |
+--------------------------------------------------------------------+ |
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* Short explanation for the XviD data strutures and routines |
Short explanation for the XviD data strutures and routines |
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* encoding part |
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* if you have further questions, visit http://www.xvid.org |
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* |
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**************************************************************/ |
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/* these are are structures/routines from xvid.h needed for encoding */ |
The encoding part |
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-------------------------------------------------------------------------- |
If you have further questions, visit http://www.xvid.org |
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+--------------------------------------------------------------------+ |
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#define API_VERSION ((1 << 16) | (0)) |
Document version : |
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$Id: xvid-encoder.txt,v 1.3 2002-06-27 14:49:05 edgomez Exp $ |
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This is the revision of the xvid.h file that you have in front of you. Check it against the library's version. |
+--------------------------------------------------------------------+ |
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| Abstract |
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+--------------------------------------------------------------------+ |
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This document presents the basic structures and API of XviD. It tries |
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to explain how to use them to obtain a simple profile compliant MPEG4 |
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stream feeding the encoder with a sequence of frames. |
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+-------------------------------------------------------------------+ |
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| Document |
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+-------------------------------------------------------------------+ |
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Chapter 1 : The XviD version |
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+-----------------------------------------------------------------+ |
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The Xvid version is defined at library compilation time using the |
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constant defined in xvid.h |
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#define API_VERSION ((2 << 16) | (1)) |
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Where 2 stands for the major XviD version, and 1 for the minor version |
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number. |
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The current version of the API is 2.1 and should be incremented each |
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time a user defined structure is modified (XVID_INIT_PARAM, |
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XVID_ENC_PARAM ... we will discuss about them later). |
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When you're writing a program/library which uses the XviD library, you |
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must check your XviD API version against the available library |
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version. We will see how to check the version number in the next |
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chapter. |
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Chapter 2 : The XVID_INIT_PARAM |
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+-----------------------------------------------------------------+ |
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-------------------------------------------------------------------------- |
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typedef struct |
typedef struct |
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{ |
{ |
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int core_build; [out] |
int core_build; [out] |
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} XVID_INIT_PARAM; |
} XVID_INIT_PARAM; |
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This is filled by xvid_init with the correct CPU flags for initialization |
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(auto-detect), unless you pass flag to it (cpu_flags!=0). Do not use that |
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unless you really know what you are doing. |
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api_version can (should) be checked against API_VERSION, to see if you |
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have the right core library. |
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Used in: xvid_init(NULL, 0, &xinit, NULL); |
Used in: xvid_init(NULL, 0, &xinit, NULL); |
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-------------------------------------------------------------------------- |
This tructure is used and filled by the xvid_init function depending |
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on the cpu_flags value. |
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List of valid flags for the cpu_flags member : |
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- XVID_CPU_MMX : cpu feature |
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- XVID_CPU_MMXEXT : cpu feature |
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- XVID_CPU_SSE : cpu feature |
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- XVID_CPU_SSE2 : cpu feature |
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- XVID_CPU_3DNOW : cpu feature |
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- XVID_CPU_3DNOWEXT : cpu feature |
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- XVID_CPU_TSC : cpu feature |
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- XVID_CPU_IA64 : cpu feature |
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- XVID_CPU_CHKONLY : command |
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- XVID_CPU_FORCE : command |
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In order to set a flag : xinit.cpu_flags |= desired_flag_constant; |
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1st case : you call xvid_init without setting the XVID_CPU_CHKONLY or |
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the XVID_CPU_FORCE flag, the xvid_init function detects auto magically |
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the host cpu features and fills the cpu_flags member. The xvid_init |
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function also performs all internal function pointers initialization |
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according to deteced features and then returns XVID_ERR_OK. |
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2nd case : you call xvid_init setting the XVID_CPU_CHKONLY flag, the |
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xvid_init function will just detect the host cpu features and return |
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XVID_ERR_OK without initializing the internal function pointers (NB: |
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The XviD library is not usable after such a call to xvid_init). |
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3rd case : you call xvid_init with the cpu_flags XVID_CPU_FORCE and |
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desired feature flags set up (eg : XVID_CPU_SSE | XVID_CPU_MMX). In |
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this case you force XviD to use the given cpu features passed in the |
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cpu_flags member. Use this if you know what you're doing. |
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NB for PowerPC archs : the ppc arch has not automatic detection, the |
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library must be compiled for a specific ppc target using the right |
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Makefile (the cpu_flags is irrevelevant for these archs). Use |
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Makefile.linuxppc for standard ppc optimized functions and |
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Makefile.linuxppc_altivec for altivec simd optimized functions. |
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NB for IA64 archs : There's optimized ia64 assembly functions provided |
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in the library, they must be forced using the |
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XVID_CPU_FORCE|XVID_CPU_IA64 pair of flags. |
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To check the XviD library version against your own XviD header file, |
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you have just to call the xvid_init function (no matter the cpu_flags) |
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and compare the returnded xinit.api_version integer with your |
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API_VERSION number. The core_build build member is not relevant at the |
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moment but is reserved for future use (when XviD would have reached a |
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certain stability in its API and releases). |
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Chapter 3 : XVID_ENC_PARAM structure |
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+-----------------------------------------------------------------+ |
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typedef struct |
typedef struct |
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{ |
{ |
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int width, height; |
int width, height; [in] |
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int fincr; // frame increment is relative to fbase |
int fincr, fbase; [in] |
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int fbase; // so each frame takes "fincr/fbase" seconds |
int rc_bitrate; [in] |
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int bitrate; // the bitrate of the target encoded stream, in bits/second |
int rc_reaction_delay_factor; [in] |
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int rc_period; // the intended rate control averaging period |
int rc_averaging_period; [in] |
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int rc_reaction_period; // the reaction period for rate control |
int rc_buffer; [in] |
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int rc_reaction_ratio; // the ratio for down/up rate control |
int max_quantizer; [in] |
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int max_quantizer; // the upper limit of the quantizer |
int min_quantizer; [in] |
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int min_quantizer; // the lower limit of the quantizer |
int max_key_interval; [in] |
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int max_key_interval; // the maximum interval between key frames |
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int motion_search; // the quality of compression ( 1=fastest, 6=best ) |
void *handle; [out] |
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int lum_masking; // lum masking on/off |
} |
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int quant_type; // 0=h.263, 1=mpeg4 |
XVID_ENC_PARAM; |
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void * handle; // [out] encoder instance handle |
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} XVID_ENC_PARAM; |
Used in: xerr = xvid_encore(NULL, XVID_ENC_CREATE, &xparam, NULL); |
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This structure has to be filled to create a new encoding instance: |
This structure has to be filled to create a new encoding instance: |
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width and height are the size of the image to be encoded. |
- width and height. |
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They have to be set to the size of the image to be encoded. |
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- fincr and fbase (<0 forces default value 25fps - [25,1]). |
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fincr and fbase are the MPEG-way of defining the framerate. |
They are the MPEG-way of defining the framerate. If you have an |
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If you have an integer framerate, say 24, 25 or 30fps, use |
integer framerate, say 24, 25 or 30fps, use fincr=1, fbase=framerate. |
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fincr=1, fbase=framerate. |
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However, if framerate is non-integer, like 23.996fps you can |
However, if framerate is non-integer, like 23.996fps you can |
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e.g. multiply with 1000, getting fincr=1000 and fbase=23996, |
e.g. multiply with 1000, getting fincr=1000 and fbase=23996, giving |
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giving you integer values again. |
you integer values again. |
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rc-parameters are for ratecontrol, you don't have to change them, |
- rc_bitrate (<0 forces default value : 900000). |
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good defaults are |
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rc_period = 2000 rc_reacton_period = 10 rc_reaction_ratio = 20 |
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min_quantizer, max_quantizer limit the range of allowed quantizers. |
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normally quantizers range is [1..31], so min=1 and max=31. |
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!!! the HIGHER the quantizer, the LOWER the quality !!! |
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!!! the HIGHER the quantizer, the HIGHER the compression ratio !!! |
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min_quant=1 is somewhat overkill, min_quant=2 is good enough |
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max_quant depends on what you encode, leave it with 31 or lower it |
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to something like 15 or 10 for better quality (but encoding with |
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very low bitrate might fail then). |
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max_key_interval is the maximum value of frames between two keyframe |
This the desired target bitrate. XviD will try to do its best to |
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respect this setting but keep in mind XviD is still in development and |
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it has not been tuned for very low bitrates. |
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- Any other rc_xxxx parameter are for the bit rate controler in order |
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to respect your rc_bitrate setting the best it can. (<0 forces |
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default values) |
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Default's are good enough and you should not change them. |
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ToDo : describe briefly their impact on the bit rate variations and |
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the rc_bitrate setting respect. |
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- min_quantizer and max_quantizer (<0 forces default values : 1,31). |
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These 2 memebers limit the range of allowed quantizers. Normally, |
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quantizer's range is [1..31], so min=1 and max=31. |
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NB : the HIGHER the quantizer, the LOWER the quality. |
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the HIGHER the quantizer, the HIGHER the compression ratio. |
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min_quant=1 is somewhat overkill, min_quant=2 is good enough max_quant |
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depends on what you encode, leave it with 31 or lower it to something |
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like 15 or 10 for better quality (but encoding with very low bitrate |
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might fail then). |
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- max_key_interval (<0 forces default value : 10*framerate == 10s) |
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This is the maximum value of frames between two keyframes |
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(I-frames). Keyframes are also inserted dynamically at scene breaks. |
(I-frames). Keyframes are also inserted dynamically at scene breaks. |
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It is important to have some keyframes, even in longer scenes, if you |
It is important to have some keyframes, even in longer scenes, if you |
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want to skip position in the resulting file, because skipping is only |
want to skip position in the resulting file, because skipping is only |
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possible from one keyframe to the next. However, keyframes are much larger |
possible from one keyframe to the next. However, keyframes are much |
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than non-keyframes, so do not use too many of them. |
larger than non-keyframes, so do not use too many of them. A value of |
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A value of framerate*10 is a good choice normally. |
framerate*10 is a good choice normally. |
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motion_search determines the quality of motion search done by the codec. |
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The better the search, the smaller the files (or the better the quality). |
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Since low modes (1-3) are hardly faster than high modes (4,5) a value of |
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5 is a good choice normally. 6 is possible, but a little slower. If you |
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want absolutely highest quality, use 6. |
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lum_masking stand for "luminance masking" which is an experimental feature. |
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It tries to compress better by using facts about the human eye. |
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You might try to switch it on and decide yourself, if you gain anything from it. |
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quant_type is technical, is changes the way coefficient are quantized. |
- handle |
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Both values are okay, though a value of 0 might be faster. |
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This is the returned internal encoder instance. |
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Used in: xerr = xvid_encore(NULL, XVID_ENC_CREATE, &xparam, NULL); |
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-------------------------------------------------------------------------- |
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Chapter 4 : the XVID_ENC_FRAME structure. |
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+-----------------------------------------------------------------+ |
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typedef struct |
typedef struct |
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{ |
{ |
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void * bitstream; // [in] bitstream ptr |
int general; [in] |
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int length; // [out] bitstream length (bytes) |
int motion; [in] |
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void *bitstream; [in] |
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int length; [out] |
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void *image; [in] |
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int colorspace; [in] |
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unsigned char *quant_intra_matrix; [in] |
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unsigned char *quant_inter_matrix; [in] |
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int quant; [in] |
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int intra; [in/out] |
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HINTINFO hint; [in/out] |
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} |
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XVID_ENC_FRAME; |
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Used in: |
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xerr = xvid_encore(enchandle, XVID_ENC_ENCODE, &xframe, &xstats); |
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This is the main structure to encode a frame, it gives hints to the |
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encoder on how to process an image. |
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- general flag member. |
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The general flag member informs XviD on general algorithm choices made |
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by the library client. |
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Valid flags : |
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- XVID_CUSTOM_QMATRIX : informs xvid to use the custom user |
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matrices. |
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- XVID_H263QUANT : informs xvid to use H263 quantization |
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algorithm. |
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- XVID_MPEGQUANT : informs xvid to use MPEG quantization |
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algorithm. |
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- XVID_HALFPEL : informs xvid to perform a half pixel motion |
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estimation. |
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void * image; // [in] image ptr |
- XVID_ADAPTIVEQUANT : informs xvid to perform an adaptative |
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int colorspace; // [in] source colorspace |
quantization. |
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int quant; // [in] frame quantizer (vbr) |
- XVID_LUMIMASKING : infroms xvid to use a lumimasking algorithm. |
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int intra; // [in] force intra frame (vbr only) |
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// [out] intra state |
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} XVID_ENC_FRAME; |
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- XVID_LATEINTRA : ??? |
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The main structure to encode a frame: image points to the picture, |
- XVID_INTERLACING : informs xvid to use the MPEG4 interlaced |
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in a format that is given by colorspace, e.g. XVID_CSP_RGB24 or |
mode. |
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XVID_CSP_YV12. |
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If you set quant=0, then the ratecontrol chooses quantizer for you. |
- XVID_TOPFIELDFIRST : ??? |
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If quant!=0, then this value is used as quantizer, so make 1<=quant<=31. |
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intra decides where the frame is going to be a keyframe or not. |
- XVID_ALTERNATESCAN : ??? |
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intra=1 means: make it a keyframe |
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intra=0 means: don't make it a keyframe |
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intra=-1 means: let encoder decide (based on contents and max_key_interval) |
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So for an ordinary encoding step, you would set quant=0 and intra=-1. |
- XVID_HINTEDME_GET : informs xvid to return Motion Estimation |
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vectors from the ME encoder algorithm. Used during a first pass. |
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The length of the MPEG4-bitstream is returned in length, and |
- XVID_HINTEDME_SET : informs xvid to use the user given motion |
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if you set intra to -1, it now contains the encoder's decision: |
estimation vectors as hints for the encoder ME algorithms. Used |
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0 for non-keyframe, |
during a 2nd pass. |
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1 for keyframe because of a scene change, |
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2 for keyframe because max_key_interval was reached. |
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Used in: xerr = xvid_encore(enchandle, XVID_ENC_ENCODE, &xframe, &xstats); |
- XVID_INTER4V : forces XviD to search a vector for each 8x8 block |
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within the 16x16 Macro Block. This mode should be used only if |
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the XVID_HALFPEL mode is activated (this could change in the |
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future). |
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- XVID_ME_ZERO : forces XviD to use the zero ME algorithm. |
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- XVID_ME_LOGARITHMIC : forces XviD to use the logarithmic |
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ME algorithm. |
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- XVID_ME_FULLSEARCH : forces XviD to use the full search ME |
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algorithm. |
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- XVID_ME_PMVFAST : forces XviD to use the PMVFAST ME algorithm. |
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- XVID_ME_EPZS : forces XviD to use the EPZS ME algorithm. |
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ToDo : fill the void entries in flags, and describe briefly each ME |
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algorithm. |
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- motion member. |
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Valid flags for 16x16 motion estimation (no XVID_INTER4V flag in the |
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general flag). |
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- PMV_ADVANCEDDIAMOND16 : XviD has a modified diamond algorithm |
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that performs a bit faster than the original one. Use this flag |
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if you want to use the speed optimized diamond serach. The |
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quality loss is not big (better quality than square search but |
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less than the normal diamond search). |
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- PMV_HALFPELDIAMOND16 : switches the search algorithm from 1 or 2 |
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full pixels precision to 1 or 2 half pixel precision. |
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- PMV_HALFPELREFINE16 : After normal diamond search, an extra |
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halfpel refinement step is performed. Should always be used if |
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XVID_HALFPEL is on, because it gives a rather big increase in |
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quality. |
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- PMV_EXTSEARCH16 : Normal PMVfast predicts one start vector and |
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does diamond search around this position. EXTSEARCH means that 2 |
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more start vectors are used: (0,0) and median predictor and |
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diamond search is done for those, too. Makes search slightly |
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slower, but quality sometimes gets better. |
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- PMV_EARLYSTOP16 : PMVfast and EPZS stop search if current best |
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is below some dynamic threshhold. No diamond search is done, |
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only halfpel refinement (if active). Without EARLYSTOP diamond |
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search is always done. That would be much slower, but not really |
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lead to better quality. |
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- PMV_QUICKSTOP16 : like EARLYSTOP, but not even halfpel |
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refinement is done. Normally worse quality, so it defaults to |
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off. Might be removed, too. |
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- PMV_UNRESTRICTED16 : "unrestricted ME" is a feature of |
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MPEG4. It's not implemented, so this flag is ignored (not even |
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checked). |
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- PMV_OVERLAPPING16 : same as unrestricted. Not implemented, nor |
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checked. |
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- PMV_USESQUARES16 : Replace the diamond search with a square |
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search. |
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Valid flags when using 4 vectors mode prediction. They have the same |
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meaning as their 16x16 counter part so we only give the list : |
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- PMV_ADVANCEDDIAMOND8 |
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- PMV_HALFPELDIAMOND8 |
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|
- PMV_HALFPELREFINE8 |
| 334 |
|
- PMV_EXTSEARCH8 |
| 335 |
|
- PMV_EARLYSTOP8 |
| 336 |
|
- PMV_QUICKSTOP8 |
| 337 |
|
- PMV_UNRESTRICTED8 |
| 338 |
|
- PMV_OVERLAPPING8 |
| 339 |
|
- PMV_USESQUARES8 |
| 340 |
|
|
| 341 |
|
- quant member. |
| 342 |
|
|
| 343 |
|
The quantizer value is used when the DCT coefficients are divided to |
| 344 |
|
zero those coefficients not important (according to the target bitrate |
| 345 |
|
not the image quality :-) |
| 346 |
|
|
| 347 |
|
Valid values : |
| 348 |
|
|
| 349 |
|
- 0 (zero) : Then the rate controler chooses the right quantizer |
| 350 |
|
for you. Tipically used in ABR encoding or first pass of a VBR |
| 351 |
|
encoding session. |
| 352 |
|
|
| 353 |
|
- != 0 : Then you force the encoder to use this specific |
| 354 |
|
quantizer value. It is clamped in the interval |
| 355 |
|
[1..31]. Tipically used during the 2nd pass of a VBR encoding |
| 356 |
|
session. |
| 357 |
|
|
| 358 |
|
- intra member. |
| 359 |
|
|
| 360 |
|
[in usage] |
| 361 |
|
The intra value decides wether the frame is going to be a keyframe or |
| 362 |
|
not. |
| 363 |
|
|
| 364 |
|
Valid values : |
| 365 |
|
|
| 366 |
|
- 1 : forces the encoder to create a keyframe. Mainly used during |
| 367 |
|
a VBR 2nd pass. |
| 368 |
|
|
| 369 |
|
- 0 : forces the encoder not to create a keyframe. Minaly used |
| 370 |
|
during a VBR second pass |
| 371 |
|
|
| 372 |
|
- -1 : let the encoder decide (based on contents and |
| 373 |
|
max_key_interval). Mainly used in ABR mode and dunring a 1st |
| 374 |
|
VBR pass. |
| 375 |
|
|
| 376 |
|
[out usage] |
| 377 |
|
|
| 378 |
|
When first set to -1, the encoder returns the effective keyframe state |
| 379 |
|
of the frame. |
| 380 |
|
|
| 381 |
|
- 0 : the resulting frame is not a keyframe |
| 382 |
|
|
| 383 |
|
- 1 : the resulting frame is a keyframe (scene change). |
| 384 |
|
|
| 385 |
|
- 2 : the resulting frame is a keyframe (max_keyframe interval |
| 386 |
|
reached) |
| 387 |
|
|
| 388 |
|
- quant_intra_matrix and quant_inter_matrix members. |
| 389 |
|
|
| 390 |
|
These are pointers to to a pair of user quantization matrices. You |
| 391 |
|
must set the general XVID_CUSTOM_QMATRIX flag to make sure XviD uses |
| 392 |
|
them. |
| 393 |
|
|
| 394 |
|
When set to NULL, the default XviD matrices are used. |
| 395 |
|
|
| 396 |
|
NB : each time the matrices change, XviD must write a header into the |
| 397 |
|
bitstream, so try not changing these matrices very often. This will |
| 398 |
|
save space. |
| 399 |
|
|
| 400 |
|
|
| 401 |
|
|
| 402 |
|
Chapter 5 : The XVID_ENC_STATS structure |
| 403 |
|
+-----------------------------------------------------------------+ |
| 404 |
|
|
|
-------------------------------------------------------------------------- |
|
| 405 |
|
|
| 406 |
typedef struct |
typedef struct |
| 407 |
{ |
{ |
| 411 |
|
|
| 412 |
} XVID_ENC_STATS; |
} XVID_ENC_STATS; |
| 413 |
|
|
| 414 |
In this structure the encoder return statistical data about the encoding |
Used in: |
| 415 |
process, e.g. to be saved for two-pass-encoding. |
xerr = xvid_encore(enchandle, XVID_ENC_ENCODE, &xframe, &xstats); |
| 416 |
quant is the quantizer chosen for this frame (if you let ratecontrol do it) |
|
| 417 |
hlength is the length of the frame's header, including motion information etc. |
In this structure the encoder return statistical data about the |
| 418 |
kblks, mblks, ublks are unused at the moment. |
encoding process, e.g. to be saved for two-pass-encoding. quant is |
| 419 |
|
the quantizer chosen for this frame (if you let ratecontrol do it) |
| 420 |
|
hlength is the length of the frame's header, including motion |
| 421 |
|
information etc. kblks, mblks, ublks are unused at the moment. |
| 422 |
|
|
| 423 |
|
|
| 424 |
|
|
| 425 |
Used in: xerr = xvid_encore(enchandle, XVID_ENC_ENCODE, &xframe, &xstats); |
Chapter 6 : The xvid_encode function |
| 426 |
|
+-----------------------------------------------------------------+ |
| 427 |
|
|
|
-------------------------------------------------------------------------- |
|
| 428 |
|
|
| 429 |
int xvid_encore(void * handle, |
int xvid_encore(void * handle, |
| 430 |
int opt, |
int opt, |
| 432 |
void * param2); |
void * param2); |
| 433 |
|
|
| 434 |
|
|
| 435 |
XviD uses a single-function API, so everything you want to do is done by |
XviD uses a single-function API, so everything you want to do is done |
| 436 |
this routine. The opt parameter chooses the behaviour of the routine: |
by this routine. The opt parameter chooses the behaviour of the |
| 437 |
|
routine: |
| 438 |
|
|
| 439 |
XVID_ENC_CREATE: create a new encoder, XVID_ENC_PARAM in param1, |
XVID_ENC_CREATE: create a new encoder, XVID_ENC_PARAM in param1, a |
| 440 |
a handle to the new encoder is returned in handle |
handle to the new encoder is returned in handle. |
| 441 |
|
|
| 442 |
XVID_ENC_ENCODE: encode one frame, XVID_ENC_FRAME-structure in param1, |
XVID_ENC_ENCODE: encode one frame, XVID_ENC_FRAME-structure in param1, |
| 443 |
XVID_ENC_STATS in param2 (or NULL, if you are not |
XVID_ENC_STATS in param2 (or NULL, if you are not interested in |
| 444 |
interested in statistical data). |
statistical data). |
| 445 |
|
|
| 446 |
XVID_DEC_DESTROY: shut down this encoder, do not use handle afterwards |
XVID_DEC_DESTROY: shut down this encoder, do not use handle afterwards. |
| 447 |
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|
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