H264 Bare stream packaging into MP4 considerations

Requirements: The Android end captures and saves a video stream of the webcam as an mp4 (recording starts when the record button is pressed).

Implementation: ffmpeg + x264 + sdl;

h264 naked stream is packaged into MP4, there are a lot of articles on the Internet, ffmpeg also has a muxing example, the general process is the same, refer to muxing.c of ffmpeg to write one. Here I write out the problems I encountered in the process. These problems have troubled me for a long time to solve. Who calls me a video white?

These three questions are actually very simple, but if you don't understand this, you will still spend a lot of time.

Zh

1, dts, pts:

Before write_frame (), every avpacket data must be set with dts, pts, because my video does not have B frames, so dts = pts. I do n’t know how to set pts at the beginning. The number of frames written is sufficient (combined with question 3);

2, sps, pps;

The naked stream I received is sps + pps + i frame is placed in a NALU, this sps is very important when saving to mp4, I did not set it at the beginning, the packaged Mp4 ordinary player could not recognize it;

The SPS is passed to the encoder when creating the encoder; the SPS is after 00 00 00 01 and does not include the code 00 00 00 01; I have not used pps. Zh

    case AVMEDIA_TYPE_VIDEO:
        c-> codec_id = codec_id;
        LOGE ("add_stream AVMEDIA_TYPE_VIDEO c-> time_base.num =% d", ost-> st-> codec-> time_base.num);
        c-> bit_rate = 400000;
        / * Resolution must be a multiple of two. * /
        c-> width = 352;
        c-> height = 288;
        / * 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. * /
        ost-> st-> time_base = (AVRational) {1, STREAM_FRAME_RATE}; / STREAM_FRAME_RATE};
        c-> time_base = ost-> st-> time_base;

        c-> gop_size = 12; / * emit one intra frame every twelve frames at most * /
        c-> pix_fmt = STREAM_PIX_FMT;
        if (c-> codec_id == AV_CODEC_ID_MPEG2VIDEO) {
            / * just for testing, we also add B frames * /
            c-> max_b_frames = 2;
        }
        if (c-> codec_id == AV_CODEC_ID_MPEG1VIDEO) {
            / * Needed to avoid using macroblocks in which some coeffs overflow.
             * This does not happen with normal video, it just happens here as
             * the motion of the chroma plane does not match the luma plane. * /
            c-> mb_decision = 2;
        }
       c-> extradata = spsinfo;
       c-> extradata_size = 10;
    break;

3, fps:

After saving to mp4, all kinds of fps came out during the debugging process. Finally, looking at muxing.c carefully, I found that it is actually very simple to set it right: after pts is incremented by 1, a very simple function solves this problem.

C-> time_base: input frame rate fps = 25: {1,25}, ost-> st-> time_base: output frame rate; I set it here as well as the input.

Zh

       packet-> pts = (ptsInc ++) ;; // * (90000 / STREAM_FRAME_RATE);
        packet-> dts = packet-> pts;
      // packet-> duration = 8/1000000;
       // packet-> pos = -1; // ptsInc;


        av_packet_rescale_ts (packet, c-> time_base, ost-> st-> time_base);
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