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歷史說(shuō)明
以往FFmpeg版本中保存視音頻流信息參數(shù)是AVStream結(jié)構(gòu)體中的AVCodecContext字段。當(dāng)前FFmpeg版本是3.4,新的版本已經(jīng)將AVStream結(jié)構(gòu)體中的AVCodecContext字段定義為廢棄屬性。因此無(wú)法像以前舊的版本直接通過(guò)如下的代碼獲取到AVCodecContext結(jié)構(gòu)體參數(shù):
AVCodecContext* pAVCodecContext = avcodec_alloc_context3(NULL);
pAVCodecContext = pAVFormatContext->streams[videoStream]->codec;
當(dāng)前版本保存視音頻流信息的結(jié)構(gòu)體AVCodecParameters,F(xiàn)Fmpeg提供了函數(shù)avcodec_parameters_to_context將音頻流信息拷貝到新的AVCodecContext結(jié)構(gòu)體中
函數(shù)說(shuō)明
將AVCodecParameters結(jié)構(gòu)體中碼流參數(shù)拷貝到AVCodecContext結(jié)構(gòu)體中,并且重新拷貝一份extradata內(nèi)容,涉及到的視頻的關(guān)鍵參數(shù)有format, width, height, codec_type等,這些參數(shù)在優(yōu)化avformat_find_stream_info函數(shù)的時(shí)候,手動(dòng)指定該參數(shù)通過(guò)InitDecoder函數(shù)解碼統(tǒng)一指定H264,分辨率是1920*1080
調(diào)用avformat_open_input打開網(wǎng)絡(luò)流后,下一步調(diào)用av_find_stream_info從網(wǎng)絡(luò)流中讀取視音頻流的信息,通過(guò)調(diào)試查看AVCodecParameters結(jié)構(gòu)體的視頻參數(shù)
int avcodec_parameters_to_context(AVCodecContext *codec,
const AVCodecParameters *par)
{
codec->codec_type = par->codec_type;//AVMEDIA_TYPE_VIDEO
codec->codec_id = par->codec_id;//AV_CODEC_ID_H264
codec->codec_tag = par->codec_tag;//0
codec->bit_rate = par->bit_rate;//0
codec->bits_per_coded_sample = par->bits_per_coded_sample;//0
codec->bits_per_raw_sample = par->bits_per_raw_sample;//8
codec->profile = par->profile;//66
codec->level = par->level;//42
switch (par->codec_type) {
case AVMEDIA_TYPE_VIDEO:
codec->pix_fmt = par->format;//12
codec->width = par->width;//1920
codec->height = par->height;//1080
codec->field_order = par->field_order;//AV_FIELD_PROGRESSIVE
codec->color_range = par->color_range;//AVCOL_RANGE_JPEG
codec->color_primaries = par->color_primaries;//AVCOL_PRI_BT709
codec->color_trc = par->color_trc;//AVCOL_TRC_BT709
codec->colorspace = par->color_space;//AVCOL_SPC_BT709
codec->chroma_sample_location = par->chroma_location;//AVCHROMA_LOC_LEFT
codec->sample_aspect_ratio = par->sample_aspect_ratio;//num=0,den=1
codec->has_b_frames = par->video_delay;//0
break;
case AVMEDIA_TYPE_AUDIO:
codec->sample_fmt = par->format;
codec->channel_layout = par->channel_layout;
codec->channels = par->channels;
codec->sample_rate = par->sample_rate;
codec->block_align = par->block_align;
codec->frame_size = par->frame_size;
codec->delay =
codec->initial_padding = par->initial_padding;
codec->trailing_padding = par->trailing_padding;
codec->seek_preroll = par->seek_preroll;
break;
case AVMEDIA_TYPE_SUBTITLE:
codec->width = par->width;
codec->height = par->height;
break;
}
//extradata保存SPS/PPS信息,重新拷貝一份到AVCodecContext中,用于解碼
if (par->extradata) {
av_freep(&codec->extradata);
codec->extradata = av_mallocz(par->extradata_size + AV_INPUT_BUFFER_PADDING_SIZE);
if (!codec->extradata)
return AVERROR(ENOMEM);
memcpy(codec->extradata, par->extradata, par->extradata_size);
codec->extradata_size = par->extradata_size;
}
return 0;
}
代碼定義
typedef struct AVStream
{
#if FF_API_LAVF_AVCTX
/**
* @deprecated use the codecpar struct instead
*/
attribute_deprecated
AVCodecContext *codec;
#endif
}
說(shuō)明:
當(dāng)手動(dòng)指定編碼格式的時(shí)候,說(shuō)明探測(cè)碼流格式的代碼是可以省略的,例如
avformat_open_input
avformat_find_stream_info
在其他章節(jié)中調(diào)用InitDecoder函數(shù)替換上面的函數(shù)
avformat_open_input缺省情況下,無(wú)法播放圖像,這個(gè)目前還在研究當(dāng)中
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