FFmpeg相机编码H264 MP4混合原子AVCC太小

Question

I tried to encode Android camera preview frame to h264, and mux to mp4 container.

I can created mp4 file successfully. But the mp4 format seems corrupted.

Use the ffprobe , I got the following error.

$ ffprobe o.mp4
[h264 @ 0x209fe50] non-existing PPS 0 referenced
[h264 @ 0x209fe50] decode_slice_header error
[h264 @ 0x209fe50] no frame!
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x209ea60] decoding for stream 0 failed
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x209ea60] Could not find codec parameters for stream 0 (Video: h264 (avc1 / 0x31637661), none, 568x320, 505 kb/s): unspecified pixel format

Then I use mp4info tool to see if the information is correct. I found this.

$ mp4info o.mp4 
mp4info version 2.0.0
o.mp4:
ReadProperties: atom 'avcC' is too small; overrun at property: configurationVersion (src/mp4atom.cpp,386)
mp4info: can't open o.mp4

By hexdump the content of file, I got this

$ xxd o.mp4 |grep -A 5 -B 5 avcC
0039170: 6331 0000 0000 0000 0001 0000 0000 0000  c1..............
0039180: 0000 0000 0000 0000 0000 0238 0140 0048  ...........8.@.H
0039190: 0000 0048 0000 0000 0000 0001 0000 0000  ...H............
00391a0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00391b0: 0000 0000 0000 0000 0000 0000 0018 ffff  ................
00391c0: 0000 0008 6176 6343 0000 0020 7374 7473  ....avcC... stts
00391d0: 0000 0000 0000 0002 0000 004f 0000 0ea6  ...........O....
00391e0: 0000 0001 0000 0000 0000 0058 7374 7373  ...........Xstss
00391f0: 0000 0000 0000 0012 0000 0001 0000 0005  ................
0039200: 0000 000a 0000 000f 0000 0014 0000 0019  ................
0039210: 0000 001e 0000 0023 0000 0028 0000 0029  .......#...(...)

If I didn't add global header to AVCodecContext ,

if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER) {
    // oc_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
}

ffprobe can detect the format without error, also ffplay can play it. But the avcC atom still not correct. Other player cannot play it.

Why the muxer didn't write the correct avcC atom?

How can I solve it?

Answer 1

You must set the extradata field in the codec context. The format is referenced here: Possible Locations for Sequence/Picture Parameter Set(s) for H.264 Stream

Answer 2

Solved. This problem only happened in the new version ffmpeg.

When call ffmpeg api avformat_write_header/av_write_tailer , it uses the data in AVStream->codecpar since AVStream->codec was marked deprecated.

And the extra data is filled after avcodec_open2 , so I need to copy extra data back to AVStream->codecpar .

stream->codecpar->extradata = av_malloc(oc_ctx->extradata_size + FF_INPUT_BUFFER_PADDING_SIZE);
stream->codecpar->extradata_size = oc_ctx->extradata_size;
memcpy(stream->codecpar->extradata, oc_ctx->extradata, oc_ctx->extradata_size);

Similar code snippet also can be found in ffmpeg project ffmpeg.c

if (!ost->st->codecpar->extradata && avctx->extradata) {
    ost->st->codecpar->extradata = av_malloc(avctx->extradata_size + FF_INPUT_BUFFER_PADDING_SIZE);
    if (!ost->st->codecpar->extradata) {
        av_log(NULL, AV_LOG_ERROR, "Could not allocate extradata buffer to copy parser data.\n");
        exit_program(1);
    }    
    ost->st->codecpar->extradata_size = avctx->extradata_size;
    memcpy(ost->st->codecpar->extradata, avctx->extradata, avctx->extradata_size);
}