- 该结构体用于描述编解码器信息
/* !!! 略有删减 */
typedef struct AVCodec {
const char *name; //编解码器名称，编码器之间和解码器之间是唯一的，但是编码器和解码器可共享同一个名字
const char *long_name; //编解码器的描述性名称，更易于阅读
enum AVMediaType type; //指明编解码器类型，视频、音频或字幕
enum AVCodecID id; //编解码器id，如AV_CODEC_ID_MJPEG，AV_CODEC_ID_H264
int capabilities;
uint8_t max_lowres; //解码器支持的低分辨率最大值
const AVRational *supported_framerates; //编解码器支持的帧率组
const enum AVPixelFormat *pix_fmts; //编解码器支持的像素格式组
const int *supported_samplerates; //编解码器支持的采样率组
const enum AVSampleFormat *sample_fmts; //编解码器支持的采样格式组
const uint64_t *channel_layouts; //编解码器支持的声道布局组
const AVClass *priv_class;
const AVProfile *profiles;
const char *wrapper_name;
int caps_internal;
int priv_data_size;
const AVCodecDefault *defaults;
const char *bsfs;
const struct AVCodecHWConfigInternal *const *hw_configs;
const uint32_t *codec_tags;
} AVCodec;
- 每一个编解码器都对应一个该结构体，这些编解码器以一个链表的形式存储；因此可以通过调用 av_codec_next() 函数获取下一个编解码器指针，以此来遍历所有的编解码器。
- 该结构体用于描述编解码器的上下文，包含了编解码器需要的参数信息。
/* !!! 略有删减 */
typedef struct AVCodecContext {
const AVClass *av_class;
int log_level_offset;
enum AVMediaType codec_type; //编解码器种类
const struct AVCodec *codec; //编解码器AVCodec
enum AVCodecID codec_id; //编解码器id，如AV_CODEC_ID_MJPEG，AV_CODEC_ID_H264
unsigned int codec_tag;
void *priv_data;
struct AVCodecInternal *internal;
void *opaque; //用户的私人数据
int64_t bit_rate; //平均比特率，由用户设置
int bit_rate_tolerance;
int global_quality; //全局编码质量
int compression_level; //编码压缩级别
#define FF_COMPRESSION_DEFAULT -1
int flags;
int flags2;
uint8_t *extradata; //一些编解码器需要的额外数据
int extradata_size; //一些编解码器需要的额外数据大小
AVRational time_base; //时间基，可将pts等时间戳转换为实际时间(秒)
int ticks_per_frame; //以time_base为单位的帧率
int delay;
/* video only */
int width, height; //帧宽高
int coded_width, coded_height; //数据流宽高，因为存在解码帧在输出前被裁减或降低分辨率
int gop_size; //编码时一组图片的数量，即I帧间隔的数量
enum AVPixelFormat pix_fmt; //像素格式
int max_b_frames; //编码时，非B帧之间最大的B帧数量
float b_quant_factor;
float b_quant_offset;
int has_b_frames;
float i_quant_factor;
float i_quant_offset;
float lumi_masking;
float temporal_cplx_masking;
float spatial_cplx_masking;
float p_masking;
float dark_masking;
int slice_count;
int *slice_offset;
AVRational sample_aspect_ratio; //帧样本的宽高比
int me_cmp;
int me_sub_cmp;
int mb_cmp;
int ildct_cmp;
int dia_size;
int last_predictor_count;
int me_pre_cmp;
int pre_dia_size;
int me_subpel_quality;
int me_range;
int slice_flags;
int mb_decision;
uint16_t *intra_matrix;
uint16_t *inter_matrix;
int intra_dc_precision;
int skip_top;
int skip_bottom;
int mb_lmin;
int mb_lmax;
int bidir_refine;
int keyint_min;
int refs;
int mv0_threshold;
enum AVColorPrimaries color_primaries;
enum AVColorTransferCharacteristic color_trc;
enum AVColorSpace colorspace; //YUV色彩空间类型
enum AVColorRange color_range;
enum AVChromaLocation chroma_sample_location;
int slices;
enum AVFieldOrder field_order;
/* audio only */
int sample_rate; //采样率
int channels; //通道数
enum AVSampleFormat sample_fmt; //采样格式
int frame_size; //每个通道一帧音频帧的采样数
int frame_number; //帧计数器
int block_align;
int cutoff; //编码时的音频截止带宽
uint64_t channel_layout; //声道布局
uint64_t request_channel_layout; //请求解码器使用该通道布局，0表示默认
enum AVAudioServiceType audio_service_type;
enum AVSampleFormat request_sample_fmt; //请求解码器使用该采用格式
int (*get_buffer2)(struct AVCodecContext *s, AVFrame *frame, int flags);
float qcompress;
float qblur;
int qmin;
int qmax;
int max_qdiff;
int rc_buffer_size;
int rc_override_count;
RcOverride *rc_override;
int64_t rc_max_rate; //编解码时最大比特率
int64_t rc_min_rate; //编解码时小比特率
float rc_max_available_vbv_use;
float rc_min_vbv_overflow_use;
int rc_initial_buffer_occupancy;
int trellis;
char *stats_out;
char *stats_in;
int workaround_bugs;
int strict_std_compliance;
int error_concealment;
int debug;
int err_recognition;
int64_t reordered_opaque;
const struct AVHWAccel *hwaccel;
void *hwaccel_context;
uint64_t error[AV_NUM_DATA_POINTERS];
int dct_algo; //DCT算法
int idct_algo; //IDCT算法
int bits_per_coded_sample; //每个样本或像素的位数
int bits_per_raw_sample;
int lowres; //低分辨率解码，1-> 1/2 size, 2->1/4 size
int thread_count;
int thread_type;
int active_thread_type;
int nsse_weight;
int profile;
int level;
#define FF_LEVEL_UNKNOWN -99
enum AVDiscard skip_loop_filter;
enum AVDiscard skip_idct;
enum AVDiscard skip_frame;
uint8_t *subtitle_header;
int subtitle_header_size;
int initial_padding;
AVRational framerate; //帧率
enum AVPixelFormat sw_pix_fmt;
AVRational pkt_timebase; //pkt_dts/pts和AVPacket.dts/pts的时间基
const AVCodecDescriptor *codec_descriptor;
int64_t pts_correction_num_faulty_pts;
int64_t pts_correction_num_faulty_dts;
int64_t pts_correction_last_pts;
int64_t pts_correction_last_dts;
char *sub_charenc;
int sub_charenc_mode;
int skip_alpha;
int seek_preroll;
uint16_t *chroma_intra_matrix;
uint8_t *dump_separator;
char *codec_whitelist;
unsigned properties;
AVPacketSideData *coded_side_data;
int nb_coded_side_data;
AVBufferRef *hw_frames_ctx;
int trailing_padding;
int64_t max_pixels; //每个图像最大接收的像素数
AVBufferRef *hw_device_ctx;
int hwaccel_flags;
int apply_cropping;
int extra_hw_frames;
int discard_damaged_percentage;
int64_t max_samples; //每个音频帧最大接收的采样数
int export_side_data;
} AVCodecContext;
-
打印AVCodec信息
void AVCodec_info(AVCodec *codec) { printf("name: %s\n", codec->name); printf("long name: %s\n", codec->long_name); if (codec->type == AVMEDIA_TYPE_VIDEO) { printf("type: VIDEO, "); } else if (codec->type == AVMEDIA_TYPE_AUDIO) { printf("type: AUDIO, "); } else { printf("type: %d, ", codec->type); } printf("codec_id: %d\n", codec->id); printf("support framerates: "); const AVRational *p_fps = codec->supported_framerates; while (p_fps != NULL) { printf("[%d %d] ; ", p_fps->num, p_fps->den); p_fps ++; } printf("\n"); printf("support pix_fmts: "); const enum AVPixelFormat *p_pixfmt = codec->pix_fmts; while (p_pixfmt != NULL && *p_pixfmt >= 0) { printf("[%d] ; ", *p_pixfmt); p_pixfmt ++; } printf("\n"); printf("support samplerates: "); const int *p_sample_rate = codec->supported_samplerates; while (p_sample_rate != NULL && *p_sample_rate >= 0) { printf("[%d] ; ", *p_sample_rate); p_sample_rate ++; } printf("\n"); printf("support sample_fmts: "); const enum AVSampleFormat *p_sample_fmt = codec->sample_fmts; while (p_sample_fmt != NULL && *p_sample_fmt >= 0) { printf("[%d] ; ", *p_sample_fmt); p_sample_fmt ++; } printf("\n"); printf("support channel_layouts: "); const uint64_t *p_ch_lay = codec->channel_layouts; while (p_ch_lay != NULL && *p_ch_lay > 0) { printf("[%lu] ; ", *p_ch_lay); p_ch_lay ++; } printf("\n\n"); } -
打印AVCodecContext信息
void AVCodecContext_info(AVCodecContext *Ctx) { if (Ctx->codec_type == AVMEDIA_TYPE_VIDEO) { printf("type: VIDEO, "); } else if (Ctx->codec_type == AVMEDIA_TYPE_AUDIO) { printf("type: AUDIO, "); } else { printf("type: %d, ", Ctx->codec_type); } printf("codec_id: %d\n", Ctx->codec_id); printf("time_base: %d, %d\n", Ctx->time_base.num, Ctx->time_base.den); printf("width: %d, height: %d, PixelFormat: %d\n", Ctx->width, Ctx->height, Ctx->pix_fmt); printf("width : height = %d : %d\n", Ctx->sample_aspect_ratio.num, Ctx->sample_aspect_ratio.den); printf("channels: %d, channel layout: %lu\n", Ctx->channels, Ctx->channel_layout); printf("sample_rate: %d, sample_fmt: %d, frame_size: %d\n", Ctx->sample_rate, Ctx->sample_fmt, Ctx->frame_size); printf("frame rate: %d, %d\n\n", Ctx->framerate.num, Ctx->framerate.den); } -
输出测试视频的AVCodec和AVCodecContext信息
int main(int argc, char **argv) { AVFormatContext *fmt_ctx = NULL; AVCodec *vDc, *aDc; AVCodecContext *vDcCtx, *aDcCtx; avformat_network_init(); avformat_open_input(&fmt_ctx, "../../output/test.mp4", NULL, NULL); avformat_find_stream_info(fmt_ctx, NULL); AVStream *st1 = fmt_ctx->streams[0]; AVStream *st2 = fmt_ctx->streams[1]; vDcCtx = avcodec_alloc_context3(NULL); aDcCtx = avcodec_alloc_context3(NULL); avcodec_parameters_to_context(vDcCtx, st1->codecpar); avcodec_parameters_to_context(aDcCtx, st2->codecpar); vDc = avcodec_find_decoder(vDcCtx->codec_id); aDc = avcodec_find_decoder(aDcCtx->codec_id); avcodec_open2(vDcCtx, vDc, NULL); avcodec_open2(aDcCtx, aDc, NULL); AVCodecContext_info(vDcCtx); AVCodecContext_info(aDcCtx); AVCodec_info(vDc); AVCodec_info(aDc); return 0; } -
输出信息如下
type: VIDEO, codec_id: 27 time_base: 0, 2 width: 1280, height: 720, PixelFormat: 0 width : height = 1 : 1 channels: 0, channel layout: 0 sample_rate: 0, sample_fmt: -1, frame_size: 0 frame rate: 0, 1 type: AUDIO, codec_id: 86018 time_base: 1, 44100 width: 0, height: 0, PixelFormat: -1 width : height = 0 : 1 channels: 2, channel layout: 3 sample_rate: 44100, sample_fmt: 8, frame_size: 1024 frame rate: 0, 1 name: h264 long name: H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10 type: VIDEO, codec_id: 27 support framerates: support pix_fmts: support samplerates: support sample_fmts: support channel_layouts: name: aac long name: AAC (Advanced Audio Coding) type: AUDIO, codec_id: 86018 support framerates: support pix_fmts: support samplerates: support sample_fmts: [8] ; support channel_layouts: [4] ; [3] ; [7] ; [263] ; [55] ; [63] ; [255] ;
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