[Libav-user] Example for recompressing a video?

jettoblack jettoblack at gmail.com
Thu Jun 7 23:43:57 CEST 2012

Hi Nicolas,
Thanks again for your time so far.  I understand what you mean and I
mistakenly thought that a compilable example would be preferred over a
limited snippet.  I put the snippet below in case you don't mind taking a
quick look again.  I would definitely appreciate any assistance you can

I believe that example code for re-compressing a compressed file (as opposed
to current examples like output-example.c that does not take a compressed
input) would be useful to a lot of other people and once I get it working I
can write a wiki article with some advice for others.  If such an example
already exists I'd love to take a look.

Anyway, here is the snippet where I think the problem is (I slightly
rearranged it to make it simpler), and if you need any context I'd be happy
to provide it:

// decode audio from pkt into srcaudio
AVFrame *srcaudio = avcodec_alloc_frame();
r = avcodec_decode_audio4(in_acodec, srcaudio, &got_audio, &pkt);

// if got_audio true, resample audio to dest format
AVFrame *destaudio = avcodec_alloc_frame();     // frame for resampled audio
destaudio->extended_data = av_malloc(sizeof(uint8_t*));
destaudio->extended_data[0] = av_malloc(audio_bufsize);

r = avresample_convert(avr, 
    (void**)destaudio->extended_data, destaudio->linesize[0], audio_bufsize, 
    (void**)srcaudio->extended_data, srcaudio->linesize[0],
// encode resampled audio
AVPacket newpkt;    // new packet for encoded output
// why does this encode succeed the first time but return -22 on subsequent
r = avcodec_encode_audio2(out_acodec, &newpkt, destaudio, &got_packet_ptr);

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