【FFmpeg】AVStream结构体
- 1.AVStream结构体的定义
-
- [1.1 AVCodecParameters *codecpar](#1.1 AVCodecParameters *codecpar)
-
- [1.1.1 AVPacketSideData *coded_side_data](#1.1.1 AVPacketSideData *coded_side_data)
- [1.1.2 enum AVColorRange color_range](#1.1.2 enum AVColorRange color_range)
- [1.1.3 enum AVColorPrimaries color_primaries](#1.1.3 enum AVColorPrimaries color_primaries)
- [1.1.4 enum AVColorTransferCharacteristic color_trc](#1.1.4 enum AVColorTransferCharacteristic color_trc)
- [1.1.5 enum AVColorSpace color_space](#1.1.5 enum AVColorSpace color_space)
- [1.1.6 enum AVChromaLocation chroma_location](#1.1.6 enum AVChromaLocation chroma_location)
- [1.2.1 enum AVDiscard discard](#1.2.1 enum AVDiscard discard)
示例工程：
【FFmpeg】调用ffmpeg库实现264软编
【FFmpeg】调用ffmpeg库实现264软解
【FFmpeg】调用ffmpeg库进行RTMP推流和拉流
【FFmpeg】调用ffmpeg库进行SDL2解码后渲染
流程分析：
【FFmpeg】编码链路上主要函数的简单分析
【FFmpeg】解码链路上主要函数的简单分析
结构体分析：
【FFmpeg】AVCodec结构体
【FFmpeg】AVCodecContext结构体
今天重读AVStream结构体，参考雷博的文章，发现主要的结构体当中的变量都有些许改变，有必要重新记录一番
1.AVStream结构体的定义
AVStream记录了视频或音频码流中的信息，定义位于libavformat\avformat.h。这里与雷博记录的内容有所不同，在早期的FFmpeg版本中，AVStream中会存储AVCodecContext结构体，但是新版本中只会存储AVCodecParameters，即编解码器的参数
c
/**
* Stream structure.
* New fields can be added to the end with minor version bumps.
* Removal, reordering and changes to existing fields require a major
* version bump.
* sizeof(AVStream) must not be used outside libav*.
*/
// 流结构
// 新字段可以添加到末尾，并伴有轻微的版本变化
// 删除、重新排序和更改现有字段需要一个主要的版本更新
// sizeof(AVStream)不能在libav*之外使用
typedef struct AVStream {
/**
* A class for @ref avoptions. Set on stream creation.
*/
// 描述当前结构体的结构体
const AVClass *av_class;
// AVFormatContext中码流的索引号
int index; /**< stream index in AVFormatContext */
/**
* Format-specific stream ID.
* decoding: set by libavformat
* encoding: set by the user, replaced by libavformat if left unset
*/
// 特定于格式的流ID
int id;
/**
* Codec parameters associated with this stream. Allocated and freed by
* libavformat in avformat_new_stream() and avformat_free_context()
* respectively.
*
* - demuxing: filled by libavformat on stream creation or in
* avformat_find_stream_info()
* - muxing: filled by the caller before avformat_write_header()
*/
// 与此流相关的编解码器参数
// 由libavformat分别在avformat_new_stream()和avformat_free_context()中分配和释放
AVCodecParameters *codecpar;
// 私有参数，常用于数据格式的强制转换
void *priv_data;
/**
* This is the fundamental unit of time (in seconds) in terms
* of which frame timestamps are represented.
*
* decoding: set by libavformat
* encoding: May be set by the caller before avformat_write_header() to
* provide a hint to the muxer about the desired timebase. In
* avformat_write_header(), the muxer will overwrite this field
* with the timebase that will actually be used for the timestamps
* written into the file (which may or may not be related to the
* user-provided one, depending on the format).
*/
// 这是表示帧时间戳的基本时间单位(以秒为单位)
/*
encoding:
可以由调用者在avformat_write_header()之前设置，以向复用器提供有关所需时基的提示
在avformat_write_header()中，muxer将用实际用于写入文件的时间戳的时间基覆盖该字段
(根据格式，它可能与用户提供的时间戳相关，也可能不相关)
*/
AVRational time_base;
/**
* Decoding: pts of the first frame of the stream in presentation order, in stream time base.
* Only set this if you are absolutely 100% sure that the value you set
* it to really is the pts of the first frame.
* This may be undefined (AV_NOPTS_VALUE).
* @note The ASF header does NOT contain a correct start_time the ASF
* demuxer must NOT set this.
*/
// 流第一帧的PTS按表示顺序，以流时间为基础
// 只有当100%确定所设置的值是第一帧的分数时才设置这个值
// 这个值可能是未定义的
// @note ASF报头没有包含正确的start_time, ASF demuxer不能设置这个
int64_t start_time;
/**
* Decoding: duration of the stream, in stream time base.
* If a source file does not specify a duration, but does specify
* a bitrate, this value will be estimated from bitrate and file size.
*
* Encoding: May be set by the caller before avformat_write_header() to
* provide a hint to the muxer about the estimated duration.
*/
// Decoding: 流持续的时间，以流的时间基
// 如果源文件没有指定持续时间，但指定了比特率，则将根据比特率和文件大小估计该值
// Encoding: 可以由调用者在avformat_write_header()之前设置，以提供有关估计持续时间的提示
int64_t duration;
// 如果流当中帧数量已知，则设置；否则默认为0
int64_t nb_frames; ///< number of frames in this stream if known or 0
/**
* Stream disposition - a combination of AV_DISPOSITION_* flags.
* - demuxing: set by libavformat when creating the stream or in
* avformat_find_stream_info().
* - muxing: may be set by the caller before avformat_write_header().
*/
// 流处置- AV_DISPOSITION_*标志的组合
// demuxing: 由libavformat在创建流或avformat_find_stream_info()中设置
// muxing: 可以在avformat_write_header()之前由调用者设置
int disposition;
// 选择可以随意丢弃且不需要解绑定的报文
enum AVDiscard discard; ///< Selects which packets can be discarded at will and do not need to be demuxed.
/**
* sample aspect ratio (0 if unknown)
* - encoding: Set by user.
* - decoding: Set by libavformat.
*/
// 样本宽高比(如果未知则为0)
AVRational sample_aspect_ratio;
// 字典类型的元数据
AVDictionary *metadata;
/**
* Average framerate
*
* - demuxing: May be set by libavformat when creating the stream or in
* avformat_find_stream_info().
* - muxing: May be set by the caller before avformat_write_header().
*/
// 平均的帧率
AVRational avg_frame_rate;
/**
* For streams with AV_DISPOSITION_ATTACHED_PIC disposition, this packet
* will contain the attached picture.
*
* decoding: set by libavformat, must not be modified by the caller.
* encoding: unused
*/
// 对于AV_DISPOSITION_ATTACHED_PIC配置的流，该数据包将包含附加的图片
AVPacket attached_pic;
#if FF_API_AVSTREAM_SIDE_DATA
/**
* An array of side data that applies to the whole stream (i.e. the
* container does not allow it to change between packets).
*
* There may be no overlap between the side data in this array and side data
* in the packets. I.e. a given side data is either exported by the muxer
* (demuxing) / set by the caller (muxing) in this array, then it never
* appears in the packets, or the side data is exported / sent through
* the packets (always in the first packet where the value becomes known or
* changes), then it does not appear in this array.
*
* - demuxing: Set by libavformat when the stream is created.
* - muxing: May be set by the caller before avformat_write_header().
*
* Freed by libavformat in avformat_free_context().
*
* @deprecated use AVStream's @ref AVCodecParameters.coded_side_data
* "codecpar side data".
*/
/*
1.应用于整个流的辅助数据数组(即容器不允许它在数据包之间改变)
2.在这个数组中的侧数据和包中的侧数据之间可能没有重叠。即，给定的侧数据要么由该数组中的
muxer (demuxing)导出/由调用者(muxing)设置，然后它永远不会出现在数据包中，
或者侧数据通过数据包导出/发送(总是在值已知或更改的第一个数据包中)，然后它不会出现在此数组中
demuxing: 在创建流时由libavformat设置
muxing: 可以在avformat_write_header()之前由调用者设置
3.在avformat_free_context()中被libavformat释放
*/
attribute_deprecated
AVPacketSideData *side_data;
/**
* The number of elements in the AVStream.side_data array.
*
* @deprecated use AVStream's @ref AVCodecParameters.nb_coded_side_data
* "codecpar side data".
*/
// AVStream中元素的数量.side_data数组
attribute_deprecated
int nb_side_data;
#endif
/**
* Flags indicating events happening on the stream, a combination of
* AVSTREAM_EVENT_FLAG_*.
*
* - demuxing: may be set by the demuxer in avformat_open_input(),
* avformat_find_stream_info() and av_read_frame(). Flags must be cleared
* by the user once the event has been handled.
* - muxing: may be set by the user after avformat_write_header(). to
* indicate a user-triggered event. The muxer will clear the flags for
* events it has handled in av_[interleaved]_write_frame().
*/
// 指示流上发生的事件的标志，AVSTREAM_EVENT_FLAG_*的组合，使用不同的位标识
/*
demuxing: 可以由avformat_open_input()， avformat_find_stream_info()和av_read_frame()中的demuxer设置。
一旦事件被处理，用户必须清除标志
muxing: 可以在avformat_write_header()之后由用户设置。表示用户触发的事件。
muxer将清除av_[interleaved]_write_frame()中处理的事件的标志。
*/
int event_flags;
/**
* - demuxing: the demuxer read new metadata from the file and updated
* AVStream.metadata accordingly
* - muxing: the user updated AVStream.metadata and wishes the muxer to write
* it into the file
*/
// demuxing: demuxer从文件中读取新的元数据并更新相应的AVStream.metadata
// muxing: 用户更新了AVStream.metadata，并希望编辑器将其写入文件
#define AVSTREAM_EVENT_FLAG_METADATA_UPDATED 0x0001
/**
* - demuxing: new packets for this stream were read from the file. This
* event is informational only and does not guarantee that new packets
* for this stream will necessarily be returned from av_read_frame().
*/
// 从文件中读取了该流的新数据包。此事件仅提供信息，不保证av_read_frame()一定会返回此流的新数据包
#define AVSTREAM_EVENT_FLAG_NEW_PACKETS (1 << 1)
/**
* Real base framerate of the stream.
* This is the lowest framerate with which all timestamps can be
* represented accurately (it is the least common multiple of all
* framerates in the stream). Note, this value is just a guess!
* For example, if the time base is 1/90000 and all frames have either
* approximately 3600 or 1800 timer ticks, then r_frame_rate will be 50/1.
*/
// 流的真实基本帧率
// 这是所有时间戳可以精确表示的最低帧率(它是流中所有帧率的最小公共倍数)。注意，这个值只是一个猜测
// 例如，如果基准时间是1/90000，并且所有帧都有大约3600或1800个计时器，那么r_frame_rate将是50/1
AVRational r_frame_rate;
/**
* Number of bits in timestamps. Used for wrapping control.
*
* - demuxing: set by libavformat
* - muxing: set by libavformat
*
*/
// 时间戳中的位数。用于包装控制
int pts_wrap_bits;
} AVStream;在AVStream之中，存储的比较关键的信息有：
（1）index：AVFormatContext中流的索引号（从这里可见AVFormatContext是包含AVStream的）
（2）id：特定于格式的流ID
（3）AVCodecParameters *codecpar：编解码器的参数
（4）AVRational avg_frame_rate：平均帧率
（5）AVPacketSideData *side_data：附加数据
（6）int event_flags：描述这个流事件的标识符
（7）AVRational r_frame_rate：基于时间基的帧率
由于FFmpeg-7.0当中的AVStream结构体中不再包含AVCodec，换成了AVCodecParameters，下面看看AVCodecParameters之中存储了什么信息
1.1 AVCodecParameters *codecpar
AVCodecParameters中记录的是编码流的一些基本属性，定义位于libavocdec\codec_par.h之中
c
/**
* This struct describes the properties of an encoded stream.
*
* sizeof(AVCodecParameters) is not a part of the public ABI, this struct must
* be allocated with avcodec_parameters_alloc() and freed with
* avcodec_parameters_free().
*/
// sizeof(AVCodecParameters)不是公共ABI的一部分，这个结构体必须用avcodec_parameters_alloc()分配，
// 并用avcodec_parameters_free()释放
typedef struct AVCodecParameters {
/**
* General type of the encoded data.
*/
// 编码数据的一般类型
enum AVMediaType codec_type;
/**
* Specific type of the encoded data (the codec used).
*/
// 编码数据的特定类型(使用的编解码器)
enum AVCodecID codec_id;
/**
* Additional information about the codec (corresponds to the AVI FOURCC).
*/
// 关于编解码器的附加信息(对应于AVI FOURCC)
uint32_t codec_tag;
/**
* Extra binary data needed for initializing the decoder, codec-dependent.
*
* Must be allocated with av_malloc() and will be freed by
* avcodec_parameters_free(). The allocated size of extradata must be at
* least extradata_size + AV_INPUT_BUFFER_PADDING_SIZE, with the padding
* bytes zeroed.
*/
// 初始化解码器所需的额外二进制数据，依赖于编解码器
// 必须由av_malloc()分配，并将由avcodec_parameters_free()释放。
// 额外数据的分配大小必须至少为extraata_size + AV_INPUT_BUFFER_PADDING_SIZE，填充字节为零
uint8_t *extradata;
/**
* Size of the extradata content in bytes.
*/
// 额外数据内容的大小，以字节为单位
int extradata_size;
/**
* Additional data associated with the entire stream.
*
* Should be allocated with av_packet_side_data_new() or
* av_packet_side_data_add(), and will be freed by avcodec_parameters_free().
*/
// 与整个流相关联的附加数据
// 应该使用av_packet_side_data_new()或av_packet_side_data_add()分配，并将由avcodec_parameters_free()释放
AVPacketSideData *coded_side_data;
/**
* Amount of entries in @ref coded_side_data.
*/
// @ref coded_side_data中的条目数量
int nb_coded_side_data;
/**
* - video: the pixel format, the value corresponds to enum AVPixelFormat.
* - audio: the sample format, the value corresponds to enum AVSampleFormat.
*/
// 【视频】pixel格式，对应于AVPixelFormat
// 【音频】采样格式，对应于AVSampleFormat
int format;
/**
* The average bitrate of the encoded data (in bits per second).
*/
// 编码数据的平均比特率(单位为比特每秒)
int64_t bit_rate;
/**
* The number of bits per sample in the codedwords.
*
* This is basically the bitrate per sample. It is mandatory for a bunch of
* formats to actually decode them. It's the number of bits for one sample in
* the actual coded bitstream.
*
* This could be for example 4 for ADPCM
* For PCM formats this matches bits_per_raw_sample
* Can be 0
*/
// 编码字中每个样本的位数
// 这基本上是每个样本的比特率。对一堆格式进行实际解码是强制性的。它是实际编码比特流中一个样本的位数
// 例如，对于ADPCM，这可能是4
// 对于PCM格式，它匹配bits_per_raw_sample
// 可以是0
int bits_per_coded_sample;
/**
* This is the number of valid bits in each output sample. If the
* sample format has more bits, the least significant bits are additional
* padding bits, which are always 0. Use right shifts to reduce the sample
* to its actual size. For example, audio formats with 24 bit samples will
* have bits_per_raw_sample set to 24, and format set to AV_SAMPLE_FMT_S32.
* To get the original sample use "(int32_t)sample >> 8"."
*
* For ADPCM this might be 12 or 16 or similar
* Can be 0
*/
// 这是每个输出样本中的有效位数。如果样本格式有更多位，最低有效位是额外的填充位，
// 它总是0。使用右移来减少样本到其实际大小。例如，具有24位采样的音频格式将
// bits_per_raw_sample设置为24，并将format设置为AV_SAMPLE_FMT_S32。
// 要获取原始样本，请使用"(int32_t)sample >> 8
// 对于ADPCM，这可能是12或16或类似
// 可以是0
int bits_per_raw_sample;
/**
* Codec-specific bitstream restrictions that the stream conforms to.
*/
// profile可以是baseline、main或high profile
int profile;
// level对应了编解码当中一些限制，例如解码时限制的mb数，解码位宽等等
int level;
/**
* Video only. The dimensions of the video frame in pixels.
*/
// 【视频】视频帧的宽度和高度
int width;
int height;
/**
* Video only. The aspect ratio (width / height) which a single pixel
* should have when displayed.
*
* When the aspect ratio is unknown / undefined, the numerator should be
* set to 0 (the denominator may have any value).
*/
// 【视频】显示单个像素时应该具有的长宽比(宽度/高度)
// 当宽高比未知/未定义时，分子应该设置为0(分母可以有任何值)
AVRational sample_aspect_ratio;
/**
* Video only. Number of frames per second, for streams with constant frame
* durations. Should be set to { 0, 1 } when some frames have differing
* durations or if the value is not known.
*
* @note This field correponds to values that are stored in codec-level
* headers and is typically overridden by container/transport-layer
* timestamps, when available. It should thus be used only as a last resort,
* when no higher-level timing information is available.
*/
// 【视频】每秒多少帧, 对于具有恒定帧持续时间的流。当某些帧有不同的持续时间或如果值未知时，应该设置为{0,1}吗
// @note 此字段对应于存储在编解码器级标头中的值，并且通常在可用时被容器/传输层时间戳覆盖
// 因此，只有在没有更高级别的计时信息时，才应将其作为最后手段使用
AVRational framerate;
/**
* Video only. The order of the fields in interlaced video.
*/
//【视频】交错视频中字段的顺序
enum AVFieldOrder field_order;
/**
* Video only. Additional colorspace characteristics.
*/
//【视频】额外的colorspace特征
enum AVColorRange color_range;
enum AVColorPrimaries color_primaries;
enum AVColorTransferCharacteristic color_trc;
enum AVColorSpace color_space;
enum AVChromaLocation chroma_location;
/**
* Video only. Number of delayed frames.
*/
//【视频】延时帧数量
int video_delay;
/**
* Audio only. The channel layout and number of channels.
*/
//【音频】声道数
AVChannelLayout ch_layout;
/**
* Audio only. The number of audio samples per second.
*/
//【音频】每秒音频样本数
int sample_rate;
/**
* Audio only. The number of bytes per coded audio frame, required by some
* formats.
*
* Corresponds to nBlockAlign in WAVEFORMATEX.
*/
//【音频】某些格式要求的每个编码音频帧的字节数
int block_align;
/**
* Audio only. Audio frame size, if known. Required by some formats to be static.
*/
//【音频】音频帧大小，需要一些格式是确定的
int frame_size;
/**
* Audio only. The amount of padding (in samples) inserted by the encoder at
* the beginning of the audio. I.e. this number of leading decoded samples
* must be discarded by the caller to get the original audio without leading
* padding.
*/
// 【音频】编码器在音频开始时插入的填充量(在样本中)
// 这个数量的前导解码样本必须被调用者丢弃，以获得没有前导填充的原始音频
int initial_padding;
/**
* Audio only. The amount of padding (in samples) appended by the encoder to
* the end of the audio. I.e. this number of decoded samples must be
* discarded by the caller from the end of the stream to get the original
* audio without any trailing padding.
*/
// 【音频】由编码器附加到音频末尾的填充量(在样本中)。
// 这个解码样本的数量必须被调用者从流的末尾丢弃，以获得没有任何尾部填充的原始音频
int trailing_padding;
/**
* Audio only. Number of samples to skip after a discontinuity.
*/
//【音频】不连续后要跳过的样本数
int seek_preroll;
} AVCodecParameters;粗略来看，AVCodecParameters之中存储的信息和AVCodecContext之间的关系更像是子集关系，AVCodecParameters只包含部分的变量，例如长宽、格式和帧率等等，AVCodecContext既包含了这些变量，还包含了如qp控制、bitrate控制、硬件编解码等等一系列变量，此外AVCodecContext之中还定义了一些函数指针，如get_format和get_buffer等。在新版本中将编解码器参数和上下文信息隔离开来，应该是不希望在stream这个级别去改变codec的一些操作，关闭这个接口。我对这里的理解是，尽管封装了操作接口和部分变量，但AVStream和AVCodecContext之间的关系应该仍然是一对一的
1.1.1 AVPacketSideData *coded_side_data
c
/**
* This structure stores auxiliary information for decoding, presenting, or
* otherwise processing the coded stream. It is typically exported by demuxers
* and encoders and can be fed to decoders and muxers either in a per packet
* basis, or as global side data (applying to the entire coded stream).
*
* Global side data is handled as follows:
* - During demuxing, it may be exported through
* @ref AVStream.codecpar.side_data "AVStream's codec parameters", which can
* then be passed as input to decoders through the
* @ref AVCodecContext.coded_side_data "decoder context's side data", for
* initialization.
* - For muxing, it can be fed through @ref AVStream.codecpar.side_data
* "AVStream's codec parameters", typically the output of encoders through
* the @ref AVCodecContext.coded_side_data "encoder context's side data", for
* initialization.
*
* Packet specific side data is handled as follows:
* - During demuxing, it may be exported through @ref AVPacket.side_data
* "AVPacket's side data", which can then be passed as input to decoders.
* - For muxing, it can be fed through @ref AVPacket.side_data "AVPacket's
* side data", typically the output of encoders.
*
* Different modules may accept or export different types of side data
* depending on media type and codec. Refer to @ref AVPacketSideDataType for a
* list of defined types and where they may be found or used.
*/
/*
1.该结构存储用于解码、表示或以其他方式处理编码流的辅助信息。它通常由解码器和编码器导出，
可以以每个包为基础馈送到解码器和复用器，也可以作为全局侧数据(适用于整个编码流)
2.全局端数据的处理方法如下:（这里感觉不是很理解？）
（1）在解复用过程中，可以通过@ref AVStream.codecpar.side_data "AVStream's codec parameters"导出，
然后可以通过@ref AVCodecContext作为输入传递给解码器，变量名为"decoder context's side data"，用于初始化。
（2）在复用过程中，可以通过@ref AVStream.codecpar "AVStream's codec parameters"提供，
通常而言，是通过@ref AVCodecContext.coded_side_data "encoder context's side data"进行输入，用于初始化
3.packet的特定的side data的处理方法如下：
（1）在解复用过程中，能够通过@ref AVPacket.side_data "AVPacket's side data"进行输出，然后可以将其作为输入传递给解码器
（2）在复用过程中，能够通过@ref AVPacket.side_data "AVPacket's side data"进行输入，常用于编码器的输出
4.根据媒体类型和编解码器的不同，不同的模块可以接受或导出不同类型的侧数据
请参阅@ref AVPacketSideDataType以获得定义类型的列表以及可以找到或使用它们的位置
*/
typedef struct AVPacketSideData {
uint8_t *data;
size_t size;
enum AVPacketSideDataType type;
} AVPacketSideData;AVPacketSideDataType的定义如下，具体记录了side data的数据类型
c
/**
* @defgroup lavc_packet_side_data AVPacketSideData
*
* Types and functions for working with AVPacketSideData.
* @{
*/
enum AVPacketSideDataType {
/**
* An AV_PKT_DATA_PALETTE side data packet contains exactly AVPALETTE_SIZE
* bytes worth of palette. This side data signals that a new palette is
* present.
*/
// AV_PKT_DATA_PALETTE端数据包包含了AVPALETTE_SIZE字节值的调色板。这个侧数据表示出现了一个新的调色板
AV_PKT_DATA_PALETTE,
/**
* The AV_PKT_DATA_NEW_EXTRADATA is used to notify the codec or the format
* that the extradata buffer was changed and the receiving side should
* act upon it appropriately. The new extradata is embedded in the side
* data buffer and should be immediately used for processing the current
* frame or packet.
*/
// AV_PKT_DATA_NEW_EXTRADATA用于通知编解码器或格式外数据缓冲区已更改，接收端应适当地对其采取行动。
// 新的额外数据被嵌入到侧数据缓冲区中，并应立即用于处理当前帧或包
AV_PKT_DATA_NEW_EXTRADATA,
/**
* An AV_PKT_DATA_PARAM_CHANGE side data packet is laid out as follows:
* @code
* u32le param_flags
* if (param_flags & AV_SIDE_DATA_PARAM_CHANGE_CHANNEL_COUNT)
* s32le channel_count
* if (param_flags & AV_SIDE_DATA_PARAM_CHANGE_CHANNEL_LAYOUT)
* u64le channel_layout
* if (param_flags & AV_SIDE_DATA_PARAM_CHANGE_SAMPLE_RATE)
* s32le sample_rate
* if (param_flags & AV_SIDE_DATA_PARAM_CHANGE_DIMENSIONS)
* s32le width
* s32le height
* @endcode
*/
AV_PKT_DATA_PARAM_CHANGE,
// ....
}1.1.2 enum AVColorRange color_range
c
/**
* Visual content value range.
*
* These values are based on definitions that can be found in multiple
* specifications, such as ITU-T BT.709 (3.4 - Quantization of RGB, luminance
* and colour-difference signals), ITU-T BT.2020 (Table 5 - Digital
* Representation) as well as ITU-T BT.2100 (Table 9 - Digital 10- and 12-bit
* integer representation). At the time of writing, the BT.2100 one is
* recommended, as it also defines the full range representation.
*
* Common definitions:
* - For RGB and luma planes such as Y in YCbCr and I in ICtCp,
* 'E' is the original value in range of 0.0 to 1.0.
* - For chroma planes such as Cb,Cr and Ct,Cp, 'E' is the original
* value in range of -0.5 to 0.5.
* - 'n' is the output bit depth.
* - For additional definitions such as rounding and clipping to valid n
* bit unsigned integer range, please refer to BT.2100 (Table 9).
*/
// 可视内容值范围
// 这些值基于多种规范中的定义，例如ITU-T BT.709 (3.4 - RGB、亮度和色差信号的量化)、ITU-T BT.2020
// (表5 -数字表示)以及ITU-T BT.2100(表9 -数字10位和12位整数表示)。在撰写本文时，推荐使用BT.2100，因为它也定义了全范围表示
// 常用定义：
//（1）对于RGB和亮度分量而言，E为原始值，范围从0.0到1.0
//（2）对于色度分量而言，E为原始值，范围从-0.5到0.5
// n是输出的比特深度
// 具体可参考BT.2100
enum AVColorRange {
AVCOL_RANGE_UNSPECIFIED = 0,
/**
* Narrow or limited range content.
*
* - For luma planes:
*
* (219 * E + 16) * 2^(n-8)
*
* F.ex. the range of 16-235 for 8 bits
*
* - For chroma planes:
*
* (224 * E + 128) * 2^(n-8)
*
* F.ex. the range of 16-240 for 8 bits
*/
AVCOL_RANGE_MPEG = 1,
/**
* Full range content.
*
* - For RGB and luma planes:
*
* (2^n - 1) * E
*
* F.ex. the range of 0-255 for 8 bits
*
* - For chroma planes:
*
* (2^n - 1) * E + 2^(n - 1)
*
* F.ex. the range of 1-255 for 8 bits
*/
AVCOL_RANGE_JPEG = 2,
AVCOL_RANGE_NB ///< Not part of ABI
};1.1.3 enum AVColorPrimaries color_primaries
c
/**
* Chromaticity coordinates of the source primaries.
* These values match the ones defined by ISO/IEC 23091-2_2019 subclause 8.1 and ITU-T H.273.
*/
// 源原色的色度坐标
// 这些值与ISO/IEC 23091-2_2019子条款8.1和ITU-T H.273定义的值相匹配
enum AVColorPrimaries {
AVCOL_PRI_RESERVED0 = 0,
AVCOL_PRI_BT709 = 1, ///< also ITU-R BT1361 / IEC 61966-2-4 / SMPTE RP 177 Annex B
AVCOL_PRI_UNSPECIFIED = 2,
AVCOL_PRI_RESERVED = 3,
AVCOL_PRI_BT470M = 4, ///< also FCC Title 47 Code of Federal Regulations 73.682 (a)(20)
AVCOL_PRI_BT470BG = 5, ///< also ITU-R BT601-6 625 / ITU-R BT1358 625 / ITU-R BT1700 625 PAL & SECAM
AVCOL_PRI_SMPTE170M = 6, ///< also ITU-R BT601-6 525 / ITU-R BT1358 525 / ITU-R BT1700 NTSC
AVCOL_PRI_SMPTE240M = 7, ///< identical to above, also called "SMPTE C" even though it uses D65
AVCOL_PRI_FILM = 8, ///< colour filters using Illuminant C
AVCOL_PRI_BT2020 = 9, ///< ITU-R BT2020
AVCOL_PRI_SMPTE428 = 10, ///< SMPTE ST 428-1 (CIE 1931 XYZ)
AVCOL_PRI_SMPTEST428_1 = AVCOL_PRI_SMPTE428,
AVCOL_PRI_SMPTE431 = 11, ///< SMPTE ST 431-2 (2011) / DCI P3
AVCOL_PRI_SMPTE432 = 12, ///< SMPTE ST 432-1 (2010) / P3 D65 / Display P3
AVCOL_PRI_EBU3213 = 22, ///< EBU Tech. 3213-E (nothing there) / one of JEDEC P22 group phosphors
AVCOL_PRI_JEDEC_P22 = AVCOL_PRI_EBU3213,
AVCOL_PRI_NB ///< Not part of ABI
};1.1.4 enum AVColorTransferCharacteristic color_trc
c
/**
* Color Transfer Characteristic.
* These values match the ones defined by ISO/IEC 23091-2_2019 subclause 8.2.
*/
// 色彩转移特性
// 这些值与ISO/IEC 23091-2_2019子条款8.2中定义的值相匹配
enum AVColorTransferCharacteristic {
AVCOL_TRC_RESERVED0 = 0,
AVCOL_TRC_BT709 = 1, ///< also ITU-R BT1361
AVCOL_TRC_UNSPECIFIED = 2,
AVCOL_TRC_RESERVED = 3,
AVCOL_TRC_GAMMA22 = 4, ///< also ITU-R BT470M / ITU-R BT1700 625 PAL & SECAM
AVCOL_TRC_GAMMA28 = 5, ///< also ITU-R BT470BG
AVCOL_TRC_SMPTE170M = 6, ///< also ITU-R BT601-6 525 or 625 / ITU-R BT1358 525 or 625 / ITU-R BT1700 NTSC
AVCOL_TRC_SMPTE240M = 7,
AVCOL_TRC_LINEAR = 8, ///< "Linear transfer characteristics"
AVCOL_TRC_LOG = 9, ///< "Logarithmic transfer characteristic (100:1 range)"
AVCOL_TRC_LOG_SQRT = 10, ///< "Logarithmic transfer characteristic (100 * Sqrt(10) : 1 range)"
AVCOL_TRC_IEC61966_2_4 = 11, ///< IEC 61966-2-4
AVCOL_TRC_BT1361_ECG = 12, ///< ITU-R BT1361 Extended Colour Gamut
AVCOL_TRC_IEC61966_2_1 = 13, ///< IEC 61966-2-1 (sRGB or sYCC)
AVCOL_TRC_BT2020_10 = 14, ///< ITU-R BT2020 for 10-bit system
AVCOL_TRC_BT2020_12 = 15, ///< ITU-R BT2020 for 12-bit system
AVCOL_TRC_SMPTE2084 = 16, ///< SMPTE ST 2084 for 10-, 12-, 14- and 16-bit systems
AVCOL_TRC_SMPTEST2084 = AVCOL_TRC_SMPTE2084,
AVCOL_TRC_SMPTE428 = 17, ///< SMPTE ST 428-1
AVCOL_TRC_SMPTEST428_1 = AVCOL_TRC_SMPTE428,
AVCOL_TRC_ARIB_STD_B67 = 18, ///< ARIB STD-B67, known as "Hybrid log-gamma"
AVCOL_TRC_NB ///< Not part of ABI
};1.1.5 enum AVColorSpace color_space
c
/**
* YUV colorspace type.
* These values match the ones defined by ISO/IEC 23091-2_2019 subclause 8.3.
*/
// YUV colorspace的类型
// 这些值与ISO/IEC 23091-2_2019子条款8.3定义的值相匹配
enum AVColorSpace {
AVCOL_SPC_RGB = 0, ///< order of coefficients is actually GBR, also IEC 61966-2-1 (sRGB), YZX and ST 428-1
AVCOL_SPC_BT709 = 1, ///< also ITU-R BT1361 / IEC 61966-2-4 xvYCC709 / derived in SMPTE RP 177 Annex B
AVCOL_SPC_UNSPECIFIED = 2,
AVCOL_SPC_RESERVED = 3, ///< reserved for future use by ITU-T and ISO/IEC just like 15-255 are
AVCOL_SPC_FCC = 4, ///< FCC Title 47 Code of Federal Regulations 73.682 (a)(20)
AVCOL_SPC_BT470BG = 5, ///< also ITU-R BT601-6 625 / ITU-R BT1358 625 / ITU-R BT1700 625 PAL & SECAM / IEC 61966-2-4 xvYCC601
AVCOL_SPC_SMPTE170M = 6, ///< also ITU-R BT601-6 525 / ITU-R BT1358 525 / ITU-R BT1700 NTSC / functionally identical to above
AVCOL_SPC_SMPTE240M = 7, ///< derived from 170M primaries and D65 white point, 170M is derived from BT470 System M's primaries
AVCOL_SPC_YCGCO = 8, ///< used by Dirac / VC-2 and H.264 FRext, see ITU-T SG16
AVCOL_SPC_YCOCG = AVCOL_SPC_YCGCO,
AVCOL_SPC_BT2020_NCL = 9, ///< ITU-R BT2020 non-constant luminance system
AVCOL_SPC_BT2020_CL = 10, ///< ITU-R BT2020 constant luminance system
AVCOL_SPC_SMPTE2085 = 11, ///< SMPTE 2085, Y'D'zD'x
AVCOL_SPC_CHROMA_DERIVED_NCL = 12, ///< Chromaticity-derived non-constant luminance system
AVCOL_SPC_CHROMA_DERIVED_CL = 13, ///< Chromaticity-derived constant luminance system
AVCOL_SPC_ICTCP = 14, ///< ITU-R BT.2100-0, ICtCp
AVCOL_SPC_NB ///< Not part of ABI
};1.1.6 enum AVChromaLocation chroma_location
c
/**
* Location of chroma samples.
*
* Illustration showing the location of the first (top left) chroma sample of the
* image, the left shows only luma, the right
* shows the location of the chroma sample, the 2 could be imagined to overlay
* each other but are drawn separately due to limitations of ASCII
*
* 1st 2nd 1st 2nd horizontal luma sample positions
* v v v v
* ______ ______
*1st luma line > |X X ... |3 4 X ... X are luma samples,
* | |1 2 1-6 are possible chroma positions
*2nd luma line > |X X ... |5 6 X ... 0 is undefined/unknown position
*/
// 色度样本的位置
// 插图显示图像的第一个(左上)色度样本的位置，左边只显示亮度，右边显示色度样本的位置，
// 可以想象这两个是相互覆盖的，但由于ASCII的限制，它们是分开绘制的
enum AVChromaLocation {
AVCHROMA_LOC_UNSPECIFIED = 0,
AVCHROMA_LOC_LEFT = 1, ///< MPEG-2/4 4:2:0, H.264 default for 4:2:0
AVCHROMA_LOC_CENTER = 2, ///< MPEG-1 4:2:0, JPEG 4:2:0, H.263 4:2:0
AVCHROMA_LOC_TOPLEFT = 3, ///< ITU-R 601, SMPTE 274M 296M S314M(DV 4:1:1), mpeg2 4:2:2
AVCHROMA_LOC_TOP = 4,
AVCHROMA_LOC_BOTTOMLEFT = 5,
AVCHROMA_LOC_BOTTOM = 6,
AVCHROMA_LOC_NB ///< Not part of ABI
};1.2.1 enum AVDiscard discard
AVDiscard结构体存在的意义是用于控制编解码过程中的数据丢弃策略，以优化性能或适应于不同的应用场景
c
/**
* @ingroup lavc_decoding
*/
enum AVDiscard{
/* We leave some space between them for extensions (drop some
* keyframes for intra-only or drop just some bidir frames). */
AVDISCARD_NONE =-16, ///< discard nothing
AVDISCARD_DEFAULT = 0, ///< discard useless packets like 0 size packets in avi
AVDISCARD_NONREF = 8, ///< discard all non reference
AVDISCARD_BIDIR = 16, ///< discard all bidirectional frames
AVDISCARD_NONINTRA= 24, ///< discard all non intra frames
AVDISCARD_NONKEY = 32, ///< discard all frames except keyframes
AVDISCARD_ALL = 48, ///< discard all
};CSDN : https://blog.csdn.net/weixin_42877471
Github : https://github.com/DoFulangChen