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  • Creating a video from images using ffmpeg libav and libx264 ?

    11 janvier 2014, par marikaner

    I am trying to create a video from images using the ffmpeg library. The images have a size of 1920x1080 and are supposed to be encoded with H.264 using a .mkv container. I have come across various problems, thinking I am getting closer to a solution, but this one I am really stuck on. With the settings I use, the first X frames (around 40, depending on what and how many images I use for the video) of my video are not encoded. avcodec_encode_video2 does not return any error (return value is 0) with got_picture_ptr = 0. The result is a video that actually looks as expected, but the first seconds are weirdly jumpy.

    So this is how I create the video file:

    // m_codecContext is an instance variable of type AVCodecContext *
// m_formatCtx is an instance variable of type AVFormatContext *

// outputFileName is a valid filename ending with .mkv
AVOutputFormat *oformat = av_guess_format(NULL, outputFileName, NULL);
if (oformat == NULL)
{
    oformat = av_guess_format("mpeg", NULL, NULL);
}

// oformat->video_codec is AV_CODEC_ID_H264
AVCodec *codec = avcodec_find_encoder(oformat->video_codec);

m_codecContext = avcodec_alloc_context3(codec);
m_codecContext->codec_id = oformat->video_codec;
m_codecContext->codec_type = AVMEDIA_TYPE_VIDEO;
m_codecContext->gop_size = 30;
m_codecContext->bit_rate = width * height * 4
m_codecContext->width = width;
m_codecContext->height = height;
m_codecContext->time_base = (AVRational){1,frameRate};
m_codecContext->max_b_frames = 1;
m_codecContext->pix_fmt = AV_PIX_FMT_YUV420P;

m_formatCtx = avformat_alloc_context();
m_formatCtx->oformat = oformat;
m_formatCtx->video_codec_id = oformat->video_codec;

snprintf(m_formatCtx->filename, sizeof(m_formatCtx->filename), "%s", outputFileName);

AVStream *videoStream = avformat_new_stream(m_formatCtx, codec);
if(!videoStream)
{
   printf("Could not allocate stream\n");
}
videoStream->codec = m_codecContext;

if(m_formatCtx->oformat->flags & AVFMT_GLOBALHEADER)
{
   m_codecContext->flags |= CODEC_FLAG_GLOBAL_HEADER;
}

avcodec_open2(m_codecContext, codec, NULL) < 0);
avio_open(&m_formatCtx->pb, outputFileName.toStdString().c_str(), AVIO_FLAG_WRITE);
avformat_write_header(m_formatCtx, NULL);

    this is how the frames are added:

    void VideoCreator::writeImageToVideo(const QSharedPointer &img, int frameIndex)
{
    AVFrame *frame = avcodec_alloc_frame();

    /* alloc image and output buffer */

    int size = m_codecContext->width * m_codecContext->height;
    int numBytes = avpicture_get_size(m_codecContext->pix_fmt, m_codecContext->width, m_codecContext->height);

    uint8_t *outbuf = (uint8_t *)malloc(numBytes);
    uint8_t *picture_buf = (uint8_t *)av_malloc(numBytes);

    int ret = av_image_fill_arrays(frame->data, frame->linesize, picture_buf, m_codecContext->pix_fmt, m_codecContext->width, m_codecContext->height, 1);

    frame->data[0] = picture_buf;
    frame->data[1] = frame->data[0] + size;
    frame->data[2] = frame->data[1] + size/4;
    frame->linesize[0] = m_codecContext->width;
    frame->linesize[1] = m_codecContext->width/2;
    frame->linesize[2] = m_codecContext->width/2;

    fflush(stdout);


    for (int y = 0; y < m_codecContext->height; y++)
    {
        for (int x = 0; x < m_codecContext->width; x++)
        {
            unsigned char b = img->bits()[(y * m_codecContext->width + x) * 4 + 0];
            unsigned char g = img->bits()[(y * m_codecContext->width + x) * 4 + 1];
            unsigned char r = img->bits()[(y * m_codecContext->width + x) * 4 + 2];

            unsigned char Y = (0.257 * r) + (0.504 * g) + (0.098 * b) + 16;

            frame->data[0][y * frame->linesize[0] + x] = Y;

            if (y % 2 == 0 && x % 2 == 0)
            {
                unsigned char V = (0.439 * r) - (0.368 * g) - (0.071 * b) + 128;
                unsigned char U = -(0.148 * r) - (0.291 * g) + (0.439 * b) + 128;

                frame->data[1][y/2 * frame->linesize[1] + x/2] = U;
                frame->data[2][y/2 * frame->linesize[2] + x/2] = V;
            }
        }
    }

    int pts = frameIndex;//(1.0 / 30.0) * 90.0 * frameIndex;

    frame->pts = pts;//av_rescale_q(m_codecContext->coded_frame->pts, m_codecContext->time_base, formatCtx->streams[0]->time_base); //(1.0 / 30.0) * 90.0 * frameIndex;

    int got_packet_ptr;
    AVPacket packet;
    av_init_packet(&packet);
    packet.data = outbuf;
    packet.size = numBytes;
    packet.stream_index = formatCtx->streams[0]->index;
    packet.flags |= AV_PKT_FLAG_KEY;
    packet.pts = packet.dts = pts;
    m_codecContext->coded_frame->pts = pts;

    ret = avcodec_encode_video2(m_codecContext, &packet, frame, &got_packet_ptr);
    if (got_packet_ptr != 0)
    {
        m_codecContext->coded_frame->pts = pts;  // Set the time stamp

        if (m_codecContext->coded_frame->pts != (0x8000000000000000LL))
        {
            pts = av_rescale_q(m_codecContext->coded_frame->pts, m_codecContext->time_base, formatCtx->streams[0]->time_base);
        }
        packet.pts = pts;
        if(m_codecContext->coded_frame->key_frame)
        {
           packet.flags |= AV_PKT_FLAG_KEY;
        }

        std::cout << "pts: " << packet.pts << ", dts: "  << packet.dts << std::endl;

        av_interleaved_write_frame(formatCtx, &packet);
        av_free_packet(&packet);
    }

    free(picture_buf);
    free(outbuf);
    av_free(frame);
    printf("\n");
}

    and this is the cleanup:

    int numBytes = avpicture_get_size(m_codecContext->pix_fmt, m_codecContext->width, m_codecContext->height);
int got_packet_ptr = 1;

int ret;
//        for(; got_packet_ptr != 0; i++)
while (got_packet_ptr)
{
    uint8_t *outbuf = (uint8_t *)malloc(numBytes);

    AVPacket packet;
    av_init_packet(&packet);
    packet.data = outbuf;
    packet.size = numBytes;

    ret = avcodec_encode_video2(m_codecContext, &packet, NULL, &got_packet_ptr);
    if (got_packet_ptr)
    {
        av_interleaved_write_frame(m_formatCtx, &packet);
    }

    av_free_packet(&packet);
    free(outbuf);
}

av_write_trailer(formatCtx);

avcodec_close(m_codecContext);
av_free(m_codecContext);
printf("\n");

    I assume it might be tied to the PTS and DTS values, but I have tried EVERYTHING. The frame index seems to make the most sense. The images are correct, I can save them to files without any problems. I am running out of ideas. I would be incredibly thankful if there was someone out there who knew better than me...

    Cheers, marikaner

    UPDATE:

    If this is of any help this is the output at the end of the video encoding:

    [libx264 @ 0x7fffc00028a0] frame I:19    Avg QP:14.24  size:312420
[libx264 @ 0x7fffc00028a0] frame P:280   Avg QP:19.16  size:148867
[libx264 @ 0x7fffc00028a0] frame B:181   Avg QP:21.31  size: 40540
[libx264 @ 0x7fffc00028a0] consecutive B-frames: 24.6% 75.4%
[libx264 @ 0x7fffc00028a0] mb I  I16..4: 30.9% 45.5% 23.7%
[libx264 @ 0x7fffc00028a0] mb P  I16..4:  4.7%  9.1%  4.5%  P16..4: 23.5% 16.6% 12.6%  0.0%  0.0%    skip:28.9%
[libx264 @ 0x7fffc00028a0] mb B  I16..4:  0.6%  0.5%  0.3%  B16..8: 26.7% 11.0%  5.5%  direct: 3.9%  skip:51.5%  L0:39.4% L1:45.0% BI:15.6%
[libx264 @ 0x7fffc00028a0] final ratefactor: 19.21
[libx264 @ 0x7fffc00028a0] 8x8 transform intra:48.2% inter:47.3%
[libx264 @ 0x7fffc00028a0] coded y,uvDC,uvAC intra: 54.9% 53.1% 30.4% inter: 25.4% 13.5% 4.2%
[libx264 @ 0x7fffc00028a0] i16 v,h,dc,p: 41% 29% 11% 19%
[libx264 @ 0x7fffc00028a0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 16% 26% 31%  3%  4%  3%  7%  3%  6%
[libx264 @ 0x7fffc00028a0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 30% 26% 14%  4%  5%  4%  7%  4%  7%
[libx264 @ 0x7fffc00028a0] i8c dc,h,v,p: 58% 26% 13%  3%
[libx264 @ 0x7fffc00028a0] Weighted P-Frames: Y:17.1% UV:3.6%
[libx264 @ 0x7fffc00028a0] ref P L0: 63.1% 21.4% 11.4%  4.1%  0.1%    
[libx264 @ 0x7fffc00028a0] ref B L0: 85.7% 14.3%
[libx264 @ 0x7fffc00028a0] kb/s:27478.30

  • How to reduce latency when streaming x264

    10 janvier 2014, par tobsen

    I would like to produce a zerolatency live video stream and play it in VLC player with as little latency as possible.

    This are the settings I currently use:

    x264_param_default_preset( &m_Params, "veryfast", "zerolatency" );

m_Params.i_threads              =   2;
m_Params.b_sliced_threads       =   true;
m_Params.i_width                =   m_SourceWidth;
m_Params.i_height               =   m_SourceHeight;

m_Params.b_intra_refresh        =   1;

m_Params.b_vfr_input            =   true;
m_Params.i_timebase_num         =   1;
m_Params.i_timebase_den         =   1000;

m_Params.i_fps_num              =   1;
m_Params.i_fps_den              =   60;

m_Params.rc.i_vbv_max_bitrate   =   512;
m_Params.rc.i_vbv_buffer_size   =   256;
m_Params.rc.f_vbv_buffer_init   =   1.1f;

m_Params.rc.i_rc_method         =   X264_RC_CRF;
m_Params.rc.f_rf_constant       =   24;
m_Params.rc.f_rf_constant_max   =   35;

m_Params.b_annexb               =   0;
m_Params.b_repeat_headers       =   0;
m_Params.b_aud                  =   0;

x264_param_apply_profile( &m_Params, "high" );

    Using those settings, I have the following issues:

    • VLC shows lots of missing frames (see screenshot, "verloren"). I am not sure if this is an issue.
    • If I set a value <200ms for the network stream delay in VLC, VLC renders a few frames and than stops to decode/render frames.
    • If I set a value >= 200ms for the network stream delay in VLC, everything looks good so far but the latency is, obviously, 200ms, which is too high.

    Question: Which settings (x264lib and VLC) should I use in order to encode and stream with as little latency as possible?

    enter image description here

  • Encoding for fastest decoding with ffmpeg

    10 janvier 2014, par nbubis

    Encoding with ffmpeg and libx264, are there presets or flags that will optimize decoding speed?

    Right now it seems that videos transcoded with similar file sizes are decoded at very different speeds using Qtkit, and I was wondering whether there are options for encoding such that the decoding speed will be maximal.

  • how to set option of ffmpeg with libx264, I,P,B order ?

    9 janvier 2014, par PeanutStars

    I'm looking for a option of ffmpeg with libx264. I want to operate it, like a hardware encoder with ordering of the fixed frame type.

    IBBPBBPBBPBBPBB..IBBPBBPBBPBBP..IBBPBBP...

    Please, give me a advice.

        #!/bin/bash

    INFILE=$1
    IFILE=$1.ts

    OPT_CRF="-g 120 -c:v libx264 -crf 18 -bf 2"
    VAL_CBR="20000k"
    OPT_COMMON="-c:v libx264 -b:v $VAL_CBR -minrate $VAL_CBR -maxrate $VAL_CBR -g 60"

    ffmpeg -i $IFILE -vf crop=1920:1088:0:16 $OPT_COMMON -acodec copy ${INFILE}.1.ts
    ffmpeg -i $IFILE -vf crop=1920:1088:1920:16 $OPT_COMMON -an ${INFILE}.2.ts
    ffmpeg -i $IFILE -vf crop=1920:1088:0:1104 $OPT_COMMON -an ${INFILE}.3.ts
    ffmpeg -i $IFILE -vf crop=1920:1088:1920:1104 $OPT_COMMON -an ${INFILE}.4.ts

  • How to set x264 encode parameters through ffmpeg AVCodecContext

    8 janvier 2014, par songqi

    I'm trying to use ffmpeg/libx264 to encode and transmit a realtime video, when I use **av_dict_set(&opts, "tune", "zerolatency", 0); ** the system works well. As the X264 encode parameters are set by ffmpeg using av_dict_set, for some research purpose I want to change them by myself. But some parameters in x264_param_t can not correspond to those parameters in AVCodecContext, such as vfr_input. So I want to know if there is a directly way to transmit parameters into X264 encoder when using libx264 in ffmpeg.

    Can anyone help me? Thanks

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