Question

I’m using a c++ library to write images captured from a webcam to an libx264 encoded mp4 file.
The encoding is working properly but when it starts it writes 40 frames to the buffer. When I close the file these frames aren’t flushed so about 6 seconds of video are left unwritten (cam is about 6fps).

So i’m calling:

out_size = libffmpeg::avcodec_encode_video( codecContext, data->VideoOutputBuffer,data->VideoOutputBufferSize, data->VideoFrame );

// if zero size, it means the image was buffered
if ( out_size > 0 )
{
//... write to file
}

I can’t see a way of accessing the images that are left in the buffer. Any ideas?

Answer 1

I’ve got this working using the following code to flush the buffer. Seems that I was searching for the wrong term – should have been “delayed frames”…

void VideoFileWriter::Flush(void)
{
if ( data != nullptr )
{
    int out_size = 0;
    int ret = 0;

    libffmpeg::AVCodecContext* c = data->VideoStream->codec;
    /* get the delayed frames */
    while (1) {
        libffmpeg::AVPacket packet;
        libffmpeg::av_init_packet(&packet);

        out_size = libffmpeg::avcodec_encode_video(c, data->VideoOutputBuffer, data->VideoOutputBufferSize, NULL);
        if (out_size < 0) {
            //fprintf(stderr, "Error encoding delayed frame %d\n", out_size);
            break;
        }
        if (out_size == 0) {
            break;
        }
        if (c->coded_frame->pts != AV_NOPTS_VALUE) {
            packet.pts = av_rescale_q(c->coded_frame->pts,
                          c->time_base,
                          data->VideoStream->time_base);
            //fprintf(stderr, "Video Frame PTS: %d\n", (int)packet.pts);
        } else {
            //fprintf(stderr, "Video Frame PTS: not set\n");
        }
        if (c->coded_frame->key_frame) {
            packet.flags |= AV_PKT_FLAG_KEY;
        }
        packet.stream_index = data->VideoStream->index;
        packet.data = data->VideoOutputBuffer;
        packet.size = out_size;

        ret = libffmpeg::av_interleaved_write_frame( data->FormatContext, &packet );
        if (ret != 0) {
            //fprintf(stderr, "Error writing delayed frame %d\n", ret);
            break;
        }
    }
    libffmpeg::avcodec_flush_buffers(data->VideoStream->codec);
}
}