FFmpeg audio API: Difference between revisions
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(→function ff_mix_init: typo) |
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/** Function to select the appropriate mixing_coeff_index_matrix | /** Function to select the appropriate mixing_coeff_index_matrix | ||
* | * | ||
* This function will be reimplemented in every codec to match its possible layouts. It | * This function will be reimplemented in every codec to match its possible layouts. It basicly will be | ||
* a cascaded switch statement. First it will switch the possible codec native configurations and after that | * a cascaded switch statement. First it will switch the possible codec native configurations and after that | ||
* the possible out_channel_mask configuration. | * the possible out_channel_mask configuration. |
Revision as of 10:44, 19 December 2007
This page is for discussion regarding the reworking of the FFmpeg audio API to accommodate the requirements needed for today's audio codecs.
Features needed
- Generalized channel mixing (SIMD optimized) - users should be able to set their own channel mixing coefficients.
- Codec alterable channel mixing coefficients - the codec should be able to set and update the channel mixing coefficients during runtime (DCA supports this feature, maybe AC-3 also).
- Output channel request function - specify the number of output channels, default should be >2 channels mapped to 2 channels
- Channel reordering - currently there are different orders depending on the codec.
- SIMD optimized interleaving
- Allow planar output - don't duplicate the interleaving code in every codec
- Support bit depths other than 16-bit - 8-bit/24-bit/32-bit/float
- Channel selection - ability to access one channel from a multichannel stream
Feature wish list
- Dolby Pro Logic Surround Sound decoding.
- Add a better FFT routine. (Would the KISS implementation be a good candidate?)
- Fixed point MDCT/FFT implementations
- Custom audio filter support. (Basing it on the video filter API ideas?)
- Proper API for enabling SIMD optimized code.
Current ideas
Threads with previous discussions in the subject:
- http://thread.gmane.org/gmane.comp.video.ffmpeg.devel/47485/focus=48097
- The thread has several ideas already implemented.
- http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/2007-November/038323.html
- Discussion of general ideas and requirements for the new API.
Mixing templates
Missing:
- How to handle non implemented mixing configuration requests ?
struct codec_mix_structe
/** This structholds the possible stream channel configurations and the possible output configurations. */ typedef struct av_codec_mix_struct { unsigned int inchannels, ///< amount of channels in the input stream unsigned int outchannels, ///< amount of channels in the requested output stream unsinged int stream_channel_mask, ///< channelmask for the input stream unsinged int out_channel_mask, ///< channelmask for the output data int8_t* mixing_coeff_index_matrix, ///< mixing matrix that correspond to the mixing configuration ///< Table with inchannels*outchannels index elements, a negative index means that the mixing coeffs should be negated. ///< For example (simplified) [1,2] would mean coeff[1]+coeff[2] while [1,-2] would mean coeff[1]-coeff[2]. } av_codec_mix_struct;
function ff_mix_init
/** Initialization routine for the libavcodec multichannel audio mixer * * The multichannel mixer does not know the "position" of the speakers and it doesn't need to either. But * depending on the mixing matrix it will unknowingly reorder channels to the native order. * * @param[in|out] mix * This is the actual mixing context. It will hold the all the information needed to perform mixing. * If the passed argument is NULL it will allocate a context. If not null it will reinit the passed * context. The mix context is of fixed size and will be large enough to support a MAX_MIX_CHANNELS * amount of channels. * * @param[in] inchannels * Number of inchannels, this is set by the input stream. This value will be stored in the mixing context. * * @param[in] outchannels * Number of outchannels, this is set by the user. This value will be stored in the mixing context. * * @param mix_table[in] * Table of av_codec_mix_struct's. * * @param[in] mixing_coeffs_table * Table with mixing coeffs, it is this table the mixing_coeff_index_matrix will refer too. It is declared as void* to * make it possible for a future addition of fixed point mixing. */ void ff_mix_init(DMIXContext* mix, unsigned int inchannels, unsigned int outchannels, unsigned int stream_channel_mask, unsigned int out_channel_mask, av_codec_mix_table* mix_table, void* mixing_coeffs_table);
//FIXME
select_mixing_matrix
//Will be merged into the ff_mix_init
/** Function to select the appropriate mixing_coeff_index_matrix * * This function will be reimplemented in every codec to match its possible layouts. It basicly will be * a cascaded switch statement. First it will switch the possible codec native configurations and after that * the possible out_channel_mask configuration. * * @param codec_channel_configuration * This is the parameter describing the possible channel configuration a codec can have. This info is taken from * the input stream. This parameter * * @param out_channel_mask * This mask will contain the user selected outchannel configuration. It will base of the dwChannelMask with the * addition of the ambisonics speaker positions. The amount of set bits will * * @returns * A mixing_coeff_index_matrix suitable for ff_mix_init will be returned. */ int8_t* select_mixing_matrix(void codec_channel_configuration, unsigned int out_channel_mask);