Decoding

Collaboration diagram for Decoding:

Modules
	Frame parsing

Macros
#define	FF_INPUT_BUFFER_PADDING_SIZE   16
	Required number of additionally allocated bytes at the end of the input bitstream for decoding. More...

Enumerations
enum	AVDiscard {   AVDISCARD_NONE =-16, AVDISCARD_DEFAULT = 0, AVDISCARD_NONREF = 8, AVDISCARD_BIDIR = 16,   AVDISCARD_NONKEY = 32, AVDISCARD_ALL = 48 }

Functions
AVCodec *	avcodec_find_decoder (enum AVCodecID id)
	Find a registered decoder with a matching codec ID. More...
AVCodec *	avcodec_find_decoder_by_name (const char *name)
	Find a registered decoder with the specified name. More...
int	avcodec_default_get_buffer2 (AVCodecContext *s, AVFrame *frame, int flags)
	The default callback for AVCodecContext.get_buffer2(). More...
unsigned	avcodec_get_edge_width (void)
	Return the amount of padding in pixels which the get_buffer callback must provide around the edge of the image for codecs which do not have the CODEC_FLAG_EMU_EDGE flag. More...
void	avcodec_align_dimensions (AVCodecContext *s, int *width, int *height)
	Modify width and height values so that they will result in a memory buffer that is acceptable for the codec if you do not use any horizontal padding. More...
void	avcodec_align_dimensions2 (AVCodecContext *s, int *width, int *height, int linesize_align[AV_NUM_DATA_POINTERS])
	Modify width and height values so that they will result in a memory buffer that is acceptable for the codec if you also ensure that all line sizes are a multiple of the respective linesize_align[i]. More...
int	avcodec_decode_audio4 (AVCodecContext *avctx, AVFrame *frame, int *got_frame_ptr, const AVPacket *avpkt)
	Decode the audio frame of size avpkt->size from avpkt->data into frame. More...
int	avcodec_decode_video2 (AVCodecContext *avctx, AVFrame *picture, int *got_picture_ptr, const AVPacket *avpkt)
	Decode the video frame of size avpkt->size from avpkt->data into picture. More...
int	avcodec_decode_subtitle2 (AVCodecContext *avctx, AVSubtitle *sub, int *got_sub_ptr, AVPacket *avpkt)
	Decode a subtitle message. More...

Detailed Description

Macro Definition Documentation

#define FF_INPUT_BUFFER_PADDING_SIZE   16

Required number of additionally allocated bytes at the end of the input bitstream for decoding.

This is mainly needed because some optimized bitstream readers read 32 or 64 bit at once and could read over the end.
Note: If the first 23 bits of the additional bytes are not 0, then damaged MPEG bitstreams could cause overread and segfault.

Definition at line 561 of file libavcodec/avcodec.h.

Referenced by a64multi_init_encoder(), aac_adtstoasc_filter(), aac_decode_frame(), aac_encode_init(), aacPlus_encode_init(), add_av_stream1(), adpcm_encode_init(), adx_read_header(), afc_read_header(), aiff_read_header(), alac_encode_init(), alloc_buffers(), apc_read_header(), ape_tag_read_field(), asf_read_stream_properties(), atrac3_decode_init(), audio_decode_example(), av_fast_padded_malloc(), av_fast_padded_mallocz(), av_grow_packet(), av_new_packet(), av_packet_from_data(), av_packet_merge_side_data(), av_packet_new_side_data(), av_packet_split_side_data(), av_parser_change(), av_parser_parse2(), av_shrink_packet(), avcodec_copy_context(), avcodec_encode_audio2(), avcodec_encode_video2(), avformat_find_stream_info(), avi_read_header(), avio_close_dyn_buf(), avui_encode_init(), cdxl_decode_frame(), celt_header(), cook_decode_init(), dca_parse_params(), decode_frame(), decode_i_frame(), decode_init(), decode_p_frame(), decode_plane(), decode_stream_header(), dshow_add_device(), dump_extradata(), dv_decode_video_segment(), encode_init(), extract_header(), extract_mpeg4_header(), Faac_encode_init(), ff_alloc_packet2(), ff_asf_parse_packet(), ff_combine_frame(), ff_generate_avci_extradata(), ff_h263_decode_frame(), ff_h264_decode_nal(), ff_id3v2_parse_apic(), ff_mjpeg_find_marker(), ff_mp4_read_dec_config_descr(), ff_mpeg_update_thread_context(), ff_parse_mpeg2_descriptor(), fixup_vorbis_headers(), flac_header(), flac_read_header(), flic_decode_frame_8BPP(), flv_get_extradata(), flv_queue_extradata(), flv_set_video_codec(), h264_mp4toannexb_filter(), h264_new_context(), handle_packets(), iff_read_header(), imx_dump_header(), init_stream(), jacosub_read_header(), latm_decode_audio_specific_config(), libopus_encode_init(), matroska_decode_buffer(), matroska_read_header(), mjpega_dump_header(), mov2textsub(), mov_read_dvc1(), mov_read_extradata(), mov_read_glbl(), mov_read_strf(), mov_read_stsz(), mov_read_wave(), mov_write_dvc1_structs(), mp3_header_compress(), mp3_header_decompress(), mp_decode_frame(), mpc8_parse_seektable(), mpc8_read_header(), mpc_read_header(), mpegts_push_data(), mss2_decode_frame(), mxf_parse_structural_metadata(), mxg_update_cache(), new_pes_packet(), noise(), ogg_new_buf(), ogg_new_stream(), ogg_read_page(), ogg_save(), oggvorbis_encode_init(), ogm_header(), oma_read_header(), opus_header(), parse_fmtp_config(), parse_packed_headers(), pcx_decode_frame(), qdm2_parse_config(), qt_rtp_parse_packet(), rdt_parse_b64buf(), read_apic(), read_header(), read_kuki_chunk(), recode_subtitle(), rl2_read_header(), rm_read_audio_stream_info(), rm_read_extradata(), sdp_parse_fmtp_config_h264(), smacker_read_header(), smush_read_header(), spdif_write_packet(), speex_header(), Stagefright_init(), submit_packet(), svq3_decode_frame(), svq3_parse_packet(), tak_read_header(), text2movsub(), theora_header(), tiff_unpack_strip(), transcode_init(), tta_read_header(), utvideo_encode_frame(), utvideo_encode_init(), vc1_decode_frame(), vc1_decode_init(), vc1_extract_headers(), vfw_read_header(), video_decode_example(), vmd_read_header(), vqf_read_header(), wma_decode_superframe(), write_frame(), wsvqa_read_header(), wsvqa_read_packet(), wv_get_value_float(), xmv_process_packet_header(), xwma_read_header(), and yop_read_header().

Enumeration Type Documentation

enum AVDiscard

Enumerator
AVDISCARD_NONE	discard nothing
AVDISCARD_DEFAULT	discard useless packets like 0 size packets in avi
AVDISCARD_NONREF	discard all non reference
AVDISCARD_BIDIR	discard all bidirectional frames
AVDISCARD_NONKEY	discard all frames except keyframes
AVDISCARD_ALL	discard all

Definition at line 591 of file libavcodec/avcodec.h.

Function Documentation

void avcodec_align_dimensions	(	AVCodecContext *	s,
		int *	width,
		int *	height
	)

Modify width and height values so that they will result in a memory buffer that is acceptable for the codec if you do not use any horizontal padding.

May only be used if a codec with CODEC_CAP_DR1 has been opened. If CODEC_FLAG_EMU_EDGE is not set, the dimensions must have been increased according to avcodec_get_edge_width() before.

Definition at line 311 of file libavcodec/utils.c.

void avcodec_align_dimensions2	(	AVCodecContext *	s,
		int *	width,
		int *	height,
		int	linesize_align[AV_NUM_DATA_POINTERS]
	)

Modify width and height values so that they will result in a memory buffer that is acceptable for the codec if you also ensure that all line sizes are a multiple of the respective linesize_align[i].

May only be used if a codec with CODEC_CAP_DR1 has been opened. If CODEC_FLAG_EMU_EDGE is not set, the dimensions must have been increased according to avcodec_get_edge_width() before.

Definition at line 191 of file libavcodec/utils.c.

Referenced by avcodec_align_dimensions(), and update_frame_pool().

int avcodec_decode_audio4	(	AVCodecContext *	avctx,
		AVFrame *	frame,
		int *	got_frame_ptr,
		const AVPacket *	avpkt
	)

Decode the audio frame of size avpkt->size from avpkt->data into frame.

Some decoders may support multiple frames in a single AVPacket. Such decoders would then just decode the first frame. In this case, avcodec_decode_audio4 has to be called again with an AVPacket containing the remaining data in order to decode the second frame, etc... Even if no frames are returned, the packet needs to be fed to the decoder with remaining data until it is completely consumed or an error occurs.

Warning

The input buffer, avpkt->data must be FF_INPUT_BUFFER_PADDING_SIZE larger than the actual read bytes because some optimized bitstream readers read 32 or 64 bits at once and could read over the end.

Note

You might have to align the input buffer. The alignment requirements depend on the CPU and the decoder.

Parameters

	avctx	the codec context
[out]	frame	The AVFrame in which to store decoded audio samples. The decoder will allocate a buffer for the decoded frame by calling the AVCodecContext.get_buffer2() callback. When AVCodecContext.refcounted_frames is set to 1, the frame is reference counted and the returned reference belongs to the caller. The caller must release the frame using av_frame_unref() when the frame is no longer needed. The caller may safely write to the frame if av_frame_is_writable() returns 1. When AVCodecContext.refcounted_frames is set to 0, the returned reference belongs to the decoder and is valid only until the next call to this function or until closing the decoder. The caller may not write to it.
[out]	got_frame_ptr	Zero if no frame could be decoded, otherwise it is non-zero.
[in]	avpkt	The input AVPacket containing the input buffer. At least avpkt->data and avpkt->size should be set. Some decoders might also require additional fields to be set.

Returns

A negative error code is returned if an error occurred during decoding, otherwise the number of bytes consumed from the input AVPacket is returned.

Definition at line 2033 of file libavcodec/utils.c.

Referenced by audio_decode_example(), audio_decode_frame(), avcodec_decode_audio3(), decode_audio(), decode_packet(), main(), movie_push_frame(), process_frame(), try_decode_frame(), and wrap().

int avcodec_decode_subtitle2	(	AVCodecContext *	avctx,
		AVSubtitle *	sub,
		int *	got_sub_ptr,
		AVPacket *	avpkt
	)

Decode a subtitle message.

Return a negative value on error, otherwise return the number of bytes used. If no subtitle could be decompressed, got_sub_ptr is zero. Otherwise, the subtitle is stored in *sub. Note that CODEC_CAP_DR1 is not available for subtitle codecs. This is for simplicity, because the performance difference is expect to be negligible and reusing a get_buffer written for video codecs would probably perform badly due to a potentially very different allocation pattern.

Parameters

	avctx	the codec context
[out]	sub	The AVSubtitle in which the decoded subtitle will be stored, must be freed with avsubtitle_free if *got_sub_ptr is set.
[in,out]	got_sub_ptr	Zero if no subtitle could be decompressed, otherwise, it is nonzero.
[in]	avpkt	The input AVPacket containing the input buffer.

Definition at line 2209 of file libavcodec/utils.c.

Referenced by subtitle_thread(), transcode_subtitles(), try_decode_frame(), and wrap().

int avcodec_decode_video2	(	AVCodecContext *	avctx,
		AVFrame *	picture,
		int *	got_picture_ptr,
		const AVPacket *	avpkt
	)

Decode the video frame of size avpkt->size from avpkt->data into picture.

Some decoders may support multiple frames in a single AVPacket, such decoders would then just decode the first frame.

Warning

The input buffer must be FF_INPUT_BUFFER_PADDING_SIZE larger than the actual read bytes because some optimized bitstream readers read 32 or 64 bits at once and could read over the end.

The end of the input buffer buf should be set to 0 to ensure that no overreading happens for damaged MPEG streams.

Note

You might have to align the input buffer avpkt->data. The alignment requirements depend on the CPU: on some CPUs it isn't necessary at all, on others it won't work at all if not aligned and on others it will work but it will have an impact on performance.

In practice, avpkt->data should have 4 byte alignment at minimum.

Note

Codecs which have the CODEC_CAP_DELAY capability set have a delay between input and output, these need to be fed with avpkt->data=NULL, avpkt->size=0 at the end to return the remaining frames.

Parameters

	avctx	the codec context
[out]	picture	The AVFrame in which the decoded video frame will be stored. Use av_frame_alloc() to get an AVFrame. The codec will allocate memory for the actual bitmap by calling the AVCodecContext.get_buffer2() callback. When AVCodecContext.refcounted_frames is set to 1, the frame is reference counted and the returned reference belongs to the caller. The caller must release the frame using av_frame_unref() when the frame is no longer needed. The caller may safely write to the frame if av_frame_is_writable() returns 1. When AVCodecContext.refcounted_frames is set to 0, the returned reference belongs to the decoder and is valid only until the next call to this function or until closing the decoder. The caller may not write to it.
[in]	avpkt	The input AVpacket containing the input buffer. You can create such packet with av_init_packet() and by then setting data and size, some decoders might in addition need other fields like flags&AV_PKT_FLAG_KEY. All decoders are designed to use the least fields possible.
[in,out]	got_picture_ptr	Zero if no frame could be decompressed, otherwise, it is nonzero.

Returns

On error a negative value is returned, otherwise the number of bytes used or zero if no frame could be decompressed.

Definition at line 1901 of file libavcodec/utils.c.

Referenced by decode_packet(), decode_video(), decode_write_frame(), ff_load_image(), get_video_frame(), main(), movie_push_frame(), process_frame(), try_decode_frame(), and wrap().

int avcodec_default_get_buffer2	(	AVCodecContext *	s,
		AVFrame *	frame,
		int	flags
	)

The default callback for AVCodecContext.get_buffer2().

It is made public so it can be called by custom get_buffer2() implementations for decoders without CODEC_CAP_DR1 set.

Definition at line 586 of file libavcodec/utils.c.

Referenced by alloc_frame_buffer(), avcodec_default_get_buffer(), avcodec_get_context_defaults3(), ff_thread_can_start_frame(), ff_thread_release_buffer(), frame_worker_thread(), submit_packet(), and thread_get_buffer_internal().

AVCodec* avcodec_find_decoder

(

enum AVCodecID

id

)

Find a registered decoder with a matching codec ID.

Parameters

id	AVCodecID of the requested decoder

Returns

A decoder if one was found, NULL otherwise.

Definition at line 2397 of file libavcodec/utils.c.

Referenced by add_input_streams(), audio_decode_example(), av_find_best_stream(), avcodec_get_name(), avcodec_get_type(), avcodec_open2(), avcodec_string(), avformat_find_stream_info(), choose_decoder(), dshow_cycle_formats(), ff_load_image(), filter_codec_opts(), find_codec_or_die(), get_sockaddr(), list_formats(), open_codec_context(), open_input_file(), open_stream(), show_codecs(), stream_component_open(), try_decode_frame(), and video_decode_example().

AVCodec* avcodec_find_decoder_by_name

(

const char *

name

)

Find a registered decoder with the specified name.

Parameters

name	name of the requested decoder

Returns

A decoder if one was found, NULL otherwise.

Definition at line 2402 of file libavcodec/utils.c.

Referenced by find_codec_or_die(), show_help_codec(), stream_component_open(), and v4l2_read_header().

unsigned avcodec_get_edge_width

(

void

)

Return the amount of padding in pixels which the get_buffer callback must provide around the edge of the image for codecs which do not have the CODEC_FLAG_EMU_EDGE flag.

Returns

Required padding in pixels.

Definition at line 172 of file libavcodec/utils.c.