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

[Andy Shaules]

I always had to decode from the latest key frame up to the desired 
stream time nal,

On 6/10/2013 2:36 PM, Faraz Khan wrote:
> Hi all,
> I'm trying to use ffmpeg as a decoder for a real-time x264 stream that 
> I'm generating. It works fine if I try to decode entire frames, but if 
> I try to decode a single NALU the decoder errors out saying 'no 
> frame'. I've tried using the parser (av_parser_parse2) but the h264 
> decoder doesnt seem to like that output either. I'm using x264 with 
> annex-b and repeat-headers on.
>
> The encoder config is as follows:
>
> x264params.b_sliced_threads = 1;
> x264params.i_slice_max_size = 1350;
> x264params.i_width = yuvSize.width;
> x264params.i_height = yuvSize.height;
> x264params.i_fps_num = 10;
> x264params.i_fps_den = 1;
> x264params.b_vfr_input = 0;
> x264params.rc.i_bitrate = 1500;
>
>  // Intra refres:
> x264params.i_keyint_max = 50000000;
> x264params.b_intra_refresh = 1;
>
> //Rate control:
>
> x264params.rc.i_rc_method = X264_RC_ABR;
> x264params.rc.i_vbv_buffer_size = 300;
> x264params.rc.i_vbv_max_bitrate = 1500;
>
> //For streaming:
> x264params.b_repeat_headers = 1;
> x264params.b_annexb = 1;
>
> x264_param_apply_profile(&x264params, "baseline");
>
>
>
> I do the encode with:
>
> int frame_size = x264_encoder_encode(x264Encoder, &nals, &i_nals, 
> &pic_in, &pic_out);
>
>
> Now, since the max slice size is 1350, each packet output is a udp 
> packet of size < MTU (this is true) and sent across the network.
>
> I iterate over the nals[i].p_payload and send them over to the ffmpeg 
> side for decoding. I receive the correct packet on the remote side.
>
> If I assemble ALL the NALUs that were output in this frame and feed it 
> directly to the decoder (even without the parser), it works fine! If I 
> feed one NALU at a time, it fails (event with the parse). I'm sending 
> it to the parser like:
>
>
> int plen = av_parser_parse2(codecParser, decoderContext, &outbuf, 
> &outside, indata,inlength,0,0,0);
>
>
> plen always reports that it consumed the entire NALU that I gave it - 
> after consuming a few NALUs, the outsize and outbuf are set to some 
> value. Feeding it into the decoder using:
>
>
>  int len = avcodec_decode_video2(decoderContext,decoderOutframe, 
> &gotpic,&avpkt);
>
>
> Results in it saying 'No frame'. Again, if avpkt.data contains the 
> entire frame (all NALUs concatenated) it will work!
>
>
> I'm obviously doing some obviously wrong - but I really cant figure 
> out why it wont decode a single NALU. Or is this a limitation in ffmpeg?
>
>
> Thanks Guys!
>
>
>
>
> --
> Faraz Khan
> Simple Collaboration Screensharing
> www.screenhero.com <http://www.screenhero.com>
>
>
> _______________________________________________
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> Libav-user at ffmpeg.org
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