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• Encoding H.264 CBR videos with FFmpeg

  3 février 2018, par Cornstalks

  I’m trying to encode a video with ffmpeg into H.264 (via the libx264 library) with a constant bit rate. I know, I know, VBR is often preferred, but for this specific job I’m required to use CBR (just as long as it’s so many kilobytes per second ; it doesn’t have to be an exact kilobytes per frame, afaik). My sample video I’m using to test is from here : http://a1408.g.akamai.net/5/1408/1388/2005110403/1a1a1ad948be278cff2d96046ad90768d848b41947aa1986/sample_iTunes.mov.zip (it comes from http://support.apple.com/kb/HT1425)

  I can get a constant bit rate when encoding the video with MPEG-4 Video (using the commands ffmpeg -i sample_iTunes.mov -b 819968 -minrate 819968 -maxrate 819968 out.mov), and the bit rate is as expected. Reading the video’s specs via the QuickTime Inspector, it’s got a data rate of 844.94 kbit/s. Cool.

  However, when I change the codec to libx264, it seems to completely ignore my bitrate requests ! The command I’m trying is "ffmpeg -i sample_iTunes.mov -vcodec libx264 -vpre medium -b 819968 -vb 819968 -minrate 819968 -maxrate 819968 -bufsize 400000 test.mov". But when I check the video’s specs via the QuickTime Inspector, it’s got a data rate of 254.74 kbit/s. WTF ? That’s not even close !

  I’ve tried changing so many parameters and adding tons of different things, and I’ve spent 2 days googling this, but I can’t seem to get it to work. If I encode the video with the MainConcept H.264 encoder, I can get a constant bitrate, but I need this to work with ffmpeg.

  If someone can help me figure out how to do CBR H.264 encoding with FFmpeg, I will love you forever !

• Assigning of dts values to encoded packets

  24 mars, par Alex

  I have a dump of H264-encoded data, which I need to put in mp4 container. I verified the validity of the encoded data by using mp4box utility against it. The mp4 file created by mp4box contained a proper 17 seconds long video. It is interesting that if I try ffmpeg to achieve the same, the resulting video is 34 seconds long and rather crappy (probably ffmpeg tries to decode video and then encode it, which results in the loss of video quality ?) Anyway, for my project I can't use command line approach and need to come up wit a programmatic way to embed the data in the mp4 container.

  



  Below is the code I use (I removed error checking for brevity. During execution all the calls succeed) :

  



  AVFormatContext* pInputFormatContext = avformat_alloc_context();
avformat_open_input(&pInputFormatContext, "Data.264", NULL, NULL);
avformat_find_stream_info(pInputFormatContext, NULL);
AVRational* pTime_base = &pInputFormatContext->streams[0]->time_base;

int nFrameRate = pInputFormatContext->streams[0]->r_frame_rate.num / pFormatCtx->streams[0]->r_frame_rate.den;
int nWidth = pInputFormatContext->streams[0]->codecpar->width;
int nHeight = pInputFormatContext->streams[0]->codecpar->height;
// nWidth = 1920, nHeight = 1080, nFrameRate = 25

// Create output objects
AVFormatContext* pOutputFormatContext = NULL;
avformat_alloc_output_context2(&pOutputFormatContext, NULL, NULL, "Destination.mp4");

AVCodec* pVideoCodec = avcodec_find_encoder(pOutputFormatContext->oformat->video_codec/*AV_CODEC_ID_264*/);
AVStream* pOutputStream = avformat_new_stream(pOutputFormatContext, NULL);
pOutputStream->id = pOutputFormatContext->nb_streams - 1;
AVCodecContext* pCodecContext = avcodec_alloc_context3(pVideoCodec);

switch (pVideoCodec->type) {
case AVMEDIA_TYPE_VIDEO:
  pCodecContext->codec_id = codec_id;
  pCodecContext->bit_rate = 400000;
  /* Resolution must be a multiple of two. */
  pCodecContext->width = nFrameWidth;
  pCodecContext->height = nFrameHeight;
  /* timebase: This is the fundamental unit of time (in seconds) in terms
  * of which frame timestamps are represented. For fixed-fps content,
  * timebase should be 1/framerate and timestamp increments should be
  * identical to 1. */
  pOutputStream->time_base.num = 1;
  pOutputStream->time_base.den = nFrameRate;
  pCodecContext->time_base = pOutputStream->time_base;
  pCodecContext->gop_size = 12; /* emit one intra frame every twelve frames at most */
  pCodecContext->pix_fmt = STREAM_PIX_FMT;
  break;
default:
  break;
}

/* copy the stream parameters to the muxer */
avcodec_parameters_from_context(pOutputStream->codecpar, pCodecContext);

avio_open(&pOutputFormatContext->pb, "Destination.mp4", AVIO_FLAG_WRITE);

// Start writing
AVDictionary* pDict = NULL;
avformat_write_header(pOutputFormatContext, &pDict);

// Process packets
AVPacket packet;
int64_t nCurrentDts = 0;
int64_t nDuration = 0;
int nReadResult = 0;

while (nReadResult == 0)
{
  nReadResult = av_read_frame(m_pInputFormatContext, &packet);
// At this point, packet.dts == AV_NOPTS_VALUE. 
// The duration field of the packet contains valid data

  packet.flags |= AV_PKT_FLAG_KEY;
  nDuration = packet.duration;
  packet.dts = nCurrentDts;
  packet.dts = av_rescale_q(nCurrentDts, pOutputFormatContext->streams[0]->codec->time_base, pOutputFormatContext->streams[0]->time_base);
  av_interleaved_write_frame(pOutputFormatContext, &packet);
  nCurrentDts += nDuration;
  nDuration += packet.duration;
  av_free_packet(&packet);
}

av_write_trailer(pOutputFormatContext);


  



  The properties for the Destination.mp4 file I receive indicate it is about 1 hour long with frame rate 0. I am sure the culprit is in the way I calculate dts values for each packet and use av_rescale_q(), but I do not have sufficient understanding of the avformat library to figure out the proper way to do it. Any help will be appreciated !

  


• C++ FFmpeg create mp4 file

  1er février 2021, par DDovzhenko

  I'm trying to create mp4 video file with FFmpeg and C++, but in result I receive broken file (windows player shows "Can't play ... 0xc00d36c4"). If I create .h264 file, it can be played with 'ffplay' and successfully converted to mp4 via CL.

  



  My code :

  



  int main() {
    char *filename = "tmp.mp4";
    AVOutputFormat *fmt;
    AVFormatContext *fctx;
    AVCodecContext *cctx;
    AVStream *st;

    av_register_all();
    avcodec_register_all();

    //auto detect the output format from the name
    fmt = av_guess_format(NULL, filename, NULL);
    if (!fmt) {
        cout << "Error av_guess_format()" << endl; system("pause"); exit(1);
    }

    if (avformat_alloc_output_context2(&fctx, fmt, NULL, filename) < 0) {
        cout << "Error avformat_alloc_output_context2()" << endl; system("pause"); exit(1);
    }


    //stream creation + parameters
    st = avformat_new_stream(fctx, 0);
    if (!st) {
        cout << "Error avformat_new_stream()" << endl; system("pause"); exit(1);
    }

    st->codecpar->codec_id = fmt->video_codec;
    st->codecpar->codec_type = AVMEDIA_TYPE_VIDEO;
    st->codecpar->width = 352;
    st->codecpar->height = 288;
    st->time_base.num = 1;
    st->time_base.den = 25;

    AVCodec *pCodec = avcodec_find_encoder(st->codecpar->codec_id);
    if (!pCodec) {
        cout << "Error avcodec_find_encoder()" << endl; system("pause"); exit(1);
    }

    cctx = avcodec_alloc_context3(pCodec);
    if (!cctx) {
        cout << "Error avcodec_alloc_context3()" << endl; system("pause"); exit(1);
    }

    avcodec_parameters_to_context(cctx, st->codecpar);
    cctx->bit_rate = 400000;
    cctx->width = 352;
    cctx->height = 288;
    cctx->time_base.num = 1;
    cctx->time_base.den = 25;
    cctx->gop_size = 12;
    cctx->pix_fmt = AV_PIX_FMT_YUV420P;
    if (st->codecpar->codec_id == AV_CODEC_ID_H264) {
        av_opt_set(cctx->priv_data, "preset", "ultrafast", 0);
    }
    if (fctx->oformat->flags & AVFMT_GLOBALHEADER) {
        cctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
    }
    avcodec_parameters_from_context(st->codecpar, cctx);

    av_dump_format(fctx, 0, filename, 1);

    //OPEN FILE + WRITE HEADER
    if (avcodec_open2(cctx, pCodec, NULL) < 0) {
        cout << "Error avcodec_open2()" << endl; system("pause"); exit(1);
    }
    if (!(fmt->flags & AVFMT_NOFILE)) {
        if (avio_open(&fctx->pb, filename, AVIO_FLAG_WRITE) < 0) {
            cout << "Error avio_open()" << endl; system("pause"); exit(1);
        }
    }
    if (avformat_write_header(fctx, NULL) < 0) {
        cout << "Error avformat_write_header()" << endl; system("pause"); exit(1);
    }


    //CREATE DUMMY VIDEO
    AVFrame *frame = av_frame_alloc();
    frame->format = cctx->pix_fmt;
    frame->width = cctx->width;
    frame->height = cctx->height;
    av_image_alloc(frame->data, frame->linesize, cctx->width, cctx->height, cctx->pix_fmt, 32);

    AVPacket pkt;
    double video_pts = 0;
    for (int i = 0; i < 50; i++) {
        video_pts = (double)cctx->time_base.num / cctx->time_base.den * 90 * i;

        for (int y = 0; y < cctx->height; y++) {
            for (int x = 0; x < cctx->width; x++) {
                frame->data[0][y * frame->linesize[0] + x] = x + y + i * 3;
                if (y < cctx->height / 2 && x < cctx->width / 2) {
                    /* Cb and Cr */
                    frame->data[1][y * frame->linesize[1] + x] = 128 + y + i * 2;
                    frame->data[2][y * frame->linesize[2] + x] = 64 + x + i * 5;
                }
            }
        }

        av_init_packet(&pkt);
        pkt.flags |= AV_PKT_FLAG_KEY;
        pkt.pts = frame->pts = video_pts;
        pkt.data = NULL;
        pkt.size = 0;
        pkt.stream_index = st->index;

        if (avcodec_send_frame(cctx, frame) < 0) {
            cout << "Error avcodec_send_frame()" << endl; system("pause"); exit(1);
        }
        if (avcodec_receive_packet(cctx, &pkt) == 0) {
            //cout << "Write frame " << to_string((int) pkt.pts) << endl;
            av_interleaved_write_frame(fctx, &pkt);
            av_packet_unref(&pkt);
        }
    }

    //DELAYED FRAMES
    for (;;) {
        avcodec_send_frame(cctx, NULL);
        if (avcodec_receive_packet(cctx, &pkt) == 0) {
            //cout << "-Write frame " << to_string((int)pkt.pts) << endl;
            av_interleaved_write_frame(fctx, &pkt);
            av_packet_unref(&pkt);
        }
        else {
            break;
        }
    }

    //FINISH
    av_write_trailer(fctx);
    if (!(fmt->flags & AVFMT_NOFILE)) {
        if (avio_close(fctx->pb) < 0) {
            cout << "Error avio_close()" << endl; system("pause"); exit(1);
        }
    }
    av_frame_free(&frame);
    avcodec_free_context(&cctx);
    avformat_free_context(fctx);

    system("pause");
    return 0;
}


  



  Output of program :

  



  Output #0, mp4, to 'tmp.mp4':
    Stream #0:0: Video: h264, yuv420p, 352x288, q=2-31, 400 kb/s, 25 tbn
[libx264 @ 0000021c4a995ba0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0000021c4a995ba0] profile Constrained Baseline, level 2.0
[libx264 @ 0000021c4a995ba0] 264 - core 152 r2851 ba24899 - H.264/MPEG-4 AVC codec - Copyleft 2003-2017 - http://www.videolan.org/x264.html - options: cabac=0 ref=1 deblock=0:0:0 analyse=0:0 me=dia subme=0 psy=1 psy_rd=1.00:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=0 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=0 threads=6 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=0 weightp=0 keyint=12 keyint_min=1 scenecut=0 intra_refresh=0 rc=abr mbtree=0 bitrate=400 ratetol=1.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=0
[libx264 @ 0000021c4a995ba0] frame I:5     Avg QP: 7.03  size:  9318
[libx264 @ 0000021c4a995ba0] frame P:45    Avg QP: 4.53  size:  4258
[libx264 @ 0000021c4a995ba0] mb I  I16..4: 100.0%  0.0%  0.0%
[libx264 @ 0000021c4a995ba0] mb P  I16..4:  0.0%  0.0%  0.0%  P16..4: 100.0%  0.0%  0.0%  0.0%  0.0%    skip: 0.0%
[libx264 @ 0000021c4a995ba0] final ratefactor: 9.11
[libx264 @ 0000021c4a995ba0] coded y,uvDC,uvAC intra: 18.9% 21.8% 14.5% inter: 7.8% 100.0% 15.5%
[libx264 @ 0000021c4a995ba0] i16 v,h,dc,p:  4%  5%  5% 86%
[libx264 @ 0000021c4a995ba0] i8c dc,h,v,p:  2%  9%  6% 82%
[libx264 @ 0000021c4a995ba0] kb/s:264.68


  



  If I will try to play mp4 file with 'ffplay' it prints :

  



  [mov,mp4,m4a,3gp,3g2,mj2 @ 00000000026bf900] Could not find codec parameters for stream 0 (Video: h264 (avc1 / 0x31637661), none, 352x288, 138953 kb/s): unspecified pixel format
[h264 @ 00000000006c6ae0] non-existing PPS 0 referenced
[h264 @ 00000000006c6ae0] decode_slice_header error
[h264 @ 00000000006c6ae0] no frame!


  



  I've spent a lot of time without success of finding issue, what could be the reason of it ?

  



  Thank for help !