[Libav-user] Decoding single NALUs from x264 programmatically (no luck even with parser), works fine with concatenated NALUs

Attila Sukosd attila.sukosd at gmail.com
Sat Jul 6 15:49:20 CEST 2013

Hi guys,

There was this thread about decoding NALUs one-by-one with parser2/decode2
and I'm having exactly the same issue.

I have x264 creating a bunch of NALUs, in annex_b and repeate_headers, and
trying to decode them one by one on the client side. When I concatenate all
the NALUs per frame into one large packet, and feed that directly into
avcodec_decode_video2, everything is fine, the decode is successful.
However, when I try to feed single NALs directly to avcodec_decode_video2,
it spits out a bunch of errors. After searching for a while on the net, I
read some place that certain types of NALs affect the rest of the data
stream, and they need to be group together.
I've tried to run the NALs through av_parser_parse2 and tried to decode the
output buffer when the output size was larger than zero, however, after
looking at the output buffer contents, it seems like while the output size
seems reasonable (around the size of the NALs or a combination of a number
of previous NALs), the output buffer content contains 3-4 bytes, and the
rest is zero.

The decoding looks like this:

 ret = av_parser_parse2(decoder->pParserCtx, decoder->pCodecCtx,
decoder->tmp_data, &outsize, buff, size, 0, 0, AV_NOPTS_VALUE);
 printf("%p buff, %p outdata, consumed %d, %d bufsize, %d outsize\n", buff,
decoder->tmp_data,ret, size, outsize);
 disp_buff(decoder->tmp_data, 50);

 if (outsize <= 0) return 0;

 decoder->avpkt.flags = AV_PKT_FLAG_KEY;
 decoder->avpkt.data = decoder->tmp_data;
 decoder->avpkt.size = outsize;

  got_picture = 0;
  if ((ret = avcodec_decode_video2(decoder->pCodecCtx, decoder->pFrame,
&got_picture, &decoder->avpkt)) < 0) {
                LOGE(__FUNCTION__, "H264 decoding failed!\n");
                return -1;

Could someone shed some light on if I'm really off the right track? or am I
just missing something very trivial?

Best Regards,

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