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ffmpeg/libx264 C API: frames dropped from end of short MP4

由 佐手、 提交于 2019-12-08 11:00:07

问题


In my C++ application, I am taking a series of JPEG images, manipulating their data using FreeImage, and then encoding the bitmaps as H264 using the ffmpeg/libx264 C API. The output is an MP4 which shows the series of 22 images at 12fps. My code is adapted from the "muxing" example that comes with ffmpeg C source code.

My problem: no matter how I tune the codec parameters, a certain number of frames at the end of the sequence which are passed to the encoder do not appear in the final output. I've set the AVCodecContext parameters like this:

//set context params
ctx->codec_id = AV_CODEC_ID_H264;
ctx->bit_rate = 4000 * 1000;
ctx->width = _width;
ctx->height = _height;
ost->st->time_base = AVRational{ 1, 12 };
ctx->time_base = ost->st->time_base;
ctx->gop_size = 1;
ctx->pix_fmt = AV_PIX_FMT_YUV420P;

I have found that the higher the gop_size the more frames are dropped from the end of the video. I can also see from the output that, with this gop size (where I'm essentially directing that all output frames be I frames) that only 9 frames are written.

I'm not sure why this is occurring. I experimented with encoding duplicate frames and making a much longer video. This resulted in no frames being dropped. I know with the ffmpeg command line tool there is a concatenation command that accomplishes what I am trying to do, but I'm not sure how to accomplish the same goal using the C API.

Here's the output I'm getting from the console:

[libx264 @ 026d81c0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2 [libx264 @ 026d81c0] profile High, level 3.1 [libx264 @ 026d81c0] 264 - core 152 r2851 ba24899 - H.264/MPEG-4 AVC codec - Cop yleft 2003-2017 - http://www.videolan.org/x264.html - options: cabac=1 ref=1 deb lock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=0 m e_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chro ma_qp_offset=-2 threads=12 lookahead_threads=2 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=0 weightp=0 keyint=1 ke yint_min=1 scenecut=40 intra_refresh=0 rc=abr mbtree=0 bitrate=4000 ratetol=1.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00 Output #0, mp4, to '....\images\c411a991-46f6-400c-8bb0-77af3738559a.mp4': Stream #0:0: Video: h264, yuv420p, 700x700, q=2-31, 4000 kb/s, 12 tbn

[libx264 @ 026d81c0] frame I:9 Avg QP:17.83 size:111058 [libx264 @ 026d81c0] mb I I16..4: 1.9% 47.7% 50.5% [libx264 @ 026d81c0] final ratefactor: 19.14 [libx264 @ 026d81c0] 8x8 transform intra:47.7% [libx264 @ 026d81c0] coded y,uvDC,uvAC intra: 98.4% 96.9% 89.5% [libx264 @ 026d81c0] i16 v,h,dc,p: 64% 6% 2% 28% [libx264 @ 026d81c0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 32% 15% 9% 5% 5% 6% 8% 10% 10% [libx264 @ 026d81c0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 28% 18% 7% 6% 8% 8% 8% 9% 8% [libx264 @ 026d81c0] i8c dc,h,v,p: 43% 22% 25% 10% [libx264 @ 026d81c0] kb/s:10661.53

Code included below:

MP4Writer.h

#ifndef MPEG_WRITER
#define MPEG_WRITER

#include <iostream>
#include <string>
#include <vector>
#include <ImgData.h>
extern "C" {
    #include <libavformat/avformat.h>
    #include <libswscale/swscale.h>
    #include <libswresample/swresample.h>
    #include <libswscale/swscale.h>
}

typedef struct OutputStream 
{
    AVStream *st;
    AVCodecContext *enc;

    //pts of the next frame that will be generated
    int64_t next_pts;
    int samples_count;

    AVFrame *frame;
    AVFrame *tmp_frame;

    float t, tincr, tincr2;

    struct SwsContext *sws_ctx;
    struct SwrContext *swr_ctx;
};

class MP4Writer {
    public:
        MP4Writer();
        void Init();
        int16_t SetOutput( const std::string & path );
        int16_t AddFrame( uint8_t * imgData );
        int16_t Write( std::vector<ImgData> & imgData );
        int16_t Finalize();
        void SetHeight( const int height ) { _height = _width = height; } //assuming 1:1 aspect ratio

    private:
        int16_t AddStream( OutputStream * ost, AVFormatContext * formatCtx, AVCodec ** codec, enum AVCodecID codecId );
        int16_t OpenVideo( AVFormatContext * formatCtx, AVCodec *codec, OutputStream * ost, AVDictionary * optArg );
        static AVFrame * AllocPicture( enum AVPixelFormat pixFmt, int width, int height );
        static AVFrame * GetVideoFrame( uint8_t * imgData, OutputStream * ost, const int width, const int height );
        static int WriteFrame( AVFormatContext * formatCtx, const AVRational * timeBase, AVStream * stream, AVPacket * packet );

        int _width;
        int _height;
        OutputStream _ost;
        AVFormatContext * _formatCtx;
        AVDictionary * _dict;
};

#endif //MPEG_WRITER

MP4Writer.cpp

#include <MP4Writer.h>
#include <algorithm>

MP4Writer::MP4Writer()
{
    _width = 0;
    _height = 0;
}

void MP4Writer::Init()
{
    av_register_all();
}

/**
 sets up output stream for the specified path.
 note that the output format is deduced automatically from the file extension passed
 @param path: output file path
 @returns: -1 = output could not be deduced, -2 = invalid codec, -3 = error opening output file,
           -4 = error writing header
*/
int16_t MP4Writer::SetOutput( const std::string & path )
{
    int error;
    AVCodec * codec;
    AVOutputFormat * format;

    _ost = OutputStream{}; //TODO reset state in a more focused way?

    //allocate output media context
    avformat_alloc_output_context2( &_formatCtx, NULL, NULL, path.c_str() );
    if ( !_formatCtx ) {
        std::cout << "could not deduce output format from file extension.  aborting" << std::endl;
        return -1;
    }
    //set format
    format = _formatCtx->oformat;
    if ( format->video_codec != AV_CODEC_ID_NONE ) {
        AddStream( &_ost, _formatCtx, &codec, format->video_codec );
    }
    else {
        std::cout << "there is no video codec set.  aborting" << std::endl;
        return -2;
    }

    OpenVideo( _formatCtx, codec, &_ost, _dict );

    av_dump_format( _formatCtx, 0, path.c_str(), 1 );

    //open output file
    if ( !( format->flags & AVFMT_NOFILE )) {
        error = avio_open( &_formatCtx->pb, path.c_str(), AVIO_FLAG_WRITE );
        if ( error < 0 ) {
            std::cout << "there was an error opening output file " << path << ".  aborting" << std::endl;
            return -3;
        }
    }

    //write header
    error = avformat_write_header( _formatCtx, &_dict );
    if ( error < 0 ) {
        std::cout << "an error occurred writing header. aborting" << std::endl;
        return -4;
    }

    return 0;
}

/**
 initialize the output stream
 @param ost: the output stream
 @param formatCtx: the context format
 @param codec: the output codec
 @param codec: the ffmpeg enumerated id of the codec
 @returns: -1 = encoder not found, -2 = stream could not be allocated, -3 = encoding context could not be allocated
*/
int16_t MP4Writer::AddStream( OutputStream * ost, AVFormatContext * formatCtx, AVCodec ** codec, enum AVCodecID codecId )
{
    AVCodecContext * ctx; //TODO not sure why this is here, could just set ost->enc directly
    int i;

    //detect the encoder
    *codec = avcodec_find_encoder( codecId );
    if ( (*codec) == NULL ) {
        std::cout << "could not find encoder.  aborting" << std::endl;
        return -1;
    }

    //allocate stream
    ost->st = avformat_new_stream( formatCtx, NULL );
    if ( ost->st == NULL ) {
        std::cout << "could not allocate stream.  aborting" << std::endl;
        return -2;
    }

    //allocate encoding context
    ost->st->id = formatCtx->nb_streams - 1;
    ctx = avcodec_alloc_context3( *codec );
    if ( ctx == NULL ) {
        std::cout << "could not allocate encoding context.  aborting" << std::endl;
        return -3;
    }

    ost->enc = ctx;

    //set context params
    ctx->codec_id = AV_CODEC_ID_H264;
    ctx->bit_rate = 4000 * 1000;
    ctx->width = _width;
    ctx->height = _height;
    ost->st->time_base = AVRational{ 1, 12 };
    ctx->time_base = ost->st->time_base;
    ctx->gop_size = 1;
    ctx->pix_fmt = AV_PIX_FMT_YUV420P;

    //if neccesary, set stream headers and formats separately
    if ( formatCtx->oformat->flags & AVFMT_GLOBALHEADER ) {
        std::cout << "setting stream and headers to be separate" << std::endl;
        ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
    }

    return 0;
}

/**
 open the video for writing
 @param formatCtx: the format context
 @param codec: output codec
 @param ost: output stream
 @param optArg: dictionary
 @return: -1 = error opening codec, -2 = allocate new frame, -3 = copy stream params
*/
int16_t MP4Writer::OpenVideo( AVFormatContext * formatCtx, AVCodec *codec, OutputStream * ost, AVDictionary * optArg )
{
    int error;
    AVCodecContext * ctx = ost->enc;
    AVDictionary * dict = NULL;
    av_dict_copy( &dict, optArg, 0 );

    //open codec
    error = avcodec_open2( ctx, codec, &dict );
    av_dict_free( &dict );
    if ( error < 0 ) {
        std::cout << "there was an error opening the codec.  aborting" << std::endl;
        return -1;
    }

    //allocate new frame
    ost->frame = AllocPicture( ctx->pix_fmt, ctx->width, ctx->height );
    if ( ost->frame == NULL ) {
        std::cout << "there was an error allocating a new frame.  aborting" << std::endl;
        return -2;
    }

    //copy steam params
    error = avcodec_parameters_from_context( ost->st->codecpar, ctx );
    if ( error < 0 ) {
        std::cout << "could not copy stream parameters.  aborting" << std::endl;
        return -3;
    }

    return 0;
}

/**
 allocate a new frame
 @param pixFmt: ffmpeg enumerated pixel format
 @param width: output width
 @param height: output height
 @returns: an inititalized frame
*/
AVFrame * MP4Writer::AllocPicture( enum AVPixelFormat pixFmt, int width, int height )
{
    AVFrame * picture;
    int error;

    //allocate the frame
    picture = av_frame_alloc();
    if ( picture == NULL ) {
        std::cout << "there was an error allocating the picture" << std::endl;
        return NULL;
    }

    picture->format = pixFmt;
    picture->width = width;
    picture->height = height;

    //allocate the frame's data buffer
    error = av_frame_get_buffer( picture, 32 );
    if ( error < 0 ) {
        std::cout << "could not allocate frame data" << std::endl;
        return NULL;
    }
    picture->pts = 0;
    return picture;
}

/**
 convert raw RGB buffer to YUV frame
 @return: frame that contains image data
*/
AVFrame * MP4Writer::GetVideoFrame( uint8_t * imgData, OutputStream * ost, const int width, const int height )
{
    int error;
    AVCodecContext * ctx = ost->enc;

    //prepare the frame
    error = av_frame_make_writable( ost->frame );
    if ( error < 0 ) {
        std::cout << "could not make frame writeable" << std::endl;
        return NULL;
    }

    //TODO set this context one time per run, or even better, one time at init
    //convert RGB to YUV
    struct SwsContext* fooContext = sws_getContext( width, height, AV_PIX_FMT_BGR24, 
        width, height, AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL );
    int inLinesize[1] = { 3 * width }; // RGB stride
    uint8_t * inData[1] = { imgData };
    int sliceHeight = sws_scale( fooContext, inData, inLinesize, 0, height, ost->frame->data, ost->frame->linesize );
    sws_freeContext( fooContext );

    ost->frame->pts = ost->next_pts++;
    //TODO does the frame need to be returned here as it is available at the class level?
    return ost->frame;
}

/**
 write frame to file
 @param formatCtx: the output format context
 @param timeBase: the framerate
 @param stream: output stream
 @param packet: data packet
 @returns: see return values for av_interleaved_write_frame
*/
int MP4Writer::WriteFrame( AVFormatContext * formatCtx, const AVRational * timeBase, AVStream * stream, AVPacket * packet )
{
    av_packet_rescale_ts( packet, *timeBase, stream->time_base );
    packet->stream_index = stream->index;

    //write compressed file to media file
    return av_interleaved_write_frame( formatCtx, packet );
}

int16_t MP4Writer::Write( std::vector<ImgData> & imgData )
{
    int16_t errorCount = 0;
    int16_t retVal = 0;
    bool countingUp = true;
    size_t i = 0;
    while ( true ) {
        //don't show first frame again when counting back down
        if ( !countingUp && i == 0 ) {
            break;
        }
        uint8_t * pixels = imgData[i].GetBits( imgData[i].mp4Input );
        AddFrame( pixels );

        //handle inc/dec without repeating last frame
        if ( countingUp ) {
            if ( i == imgData.size() -1 ) {
                countingUp = false;
                i--;
            }
            else {
                i++;
            }
        }
        else {
            i--;
        }
    }
    Finalize();
    return 0; //TODO return error code
}

/**
 add another frame to output video
 @param imgData: the raw image data
 @returns -1 = error encoding video frame, -2 = error writing frame
*/
int16_t MP4Writer::AddFrame( uint8_t * imgData )
{
    int error;
    AVCodecContext * ctx;
    AVFrame * frame;
    int gotPacket = 0;
    AVPacket pkt = { 0 };

    ctx = _ost.enc;
    av_init_packet( &pkt );

    frame = GetVideoFrame( imgData, &_ost, _width, _height );

    //encode the image
    error = avcodec_encode_video2( ctx, &pkt, frame, &gotPacket );
    if ( error < 0 ) {
        std::cout << "there was an error encoding the video frame" << std::endl;
        return -1;
    }

    //write the frame.  NOTE: this doesn't kick in until the encoder has received a certain number of frames
    if ( gotPacket ) {
        error = WriteFrame( _formatCtx, &ctx->time_base, _ost.st, &pkt );
        if ( error < 0 ) {
            std::cout << "the video frame could not be written" << std::endl;
            return -2;
        }
    }
    return 0;
}

/**
 finalize output video and cleanup
*/
int16_t MP4Writer::Finalize()
{
    av_write_trailer( _formatCtx );
    avcodec_free_context( &_ost.enc );
    av_frame_free( &_ost.frame);
    av_frame_free( &_ost.tmp_frame );
    avio_closep( &_formatCtx->pb );
    avformat_free_context( _formatCtx );
    sws_freeContext( _ost.sws_ctx );
    swr_free( &_ost.swr_ctx);
    return 0;
}

usage

#include <FreeImage.h>
#include <MP4Writer.h>
#include <vector>

struct ImgData
{
    unsigned int width;
    unsigned int height;
    std::string path;
    FIBITMAP * mp4Input;

    uint8_t * GetBits( FIBITMAP * bmp ) { return FreeImage_GetBits( bmp ); }
};

int main()
{
     std::vector<ImgData> imgDataVec;
     //load images and push to imgDataVec
     MP4Writer mp4Writer;
     mp4Writer.SetHeight( 1200 ); //assumes 1:1 aspect ratio
     mp4Writer.Init();
     mp4Writer.SetOutput( "test.mp4" );
     mp4Writer.Write( imgDataVec );
}

回答1:


I don't see codec being flushed anywhere in that code. You need to flush the codecs before writing trailer etc, so that incomplete GOPs and frames delayed for whatever else reason are forced out from the codecs. See any of encoding examples included in ffmpeg docs for the correct way to do it (e.g. https://github.com/FFmpeg/FFmpeg/blob/6d7192bcb7bbab17dc194e8dbb56c208bced0a92/doc/examples/encode_video.c#L166).



来源：https://stackoverflow.com/questions/45177897/ffmpeg-libx264-c-api-frames-dropped-from-end-of-short-mp4

标签
c++
c
ffmpeg
mp4
libx264
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