[Libav-user] AVFormatContext buffer flush

Shawn Donnelly scdmusic at gmail.com
Wed Feb 27 14:19:15 CET 2013

I have set up a custom AVIOContext that takes a callback function and
writes out data to a buffer.

static int WritePacket(void *opaque, uint8_t *pBuffer, int pBufferSize) {
    printf("Writen to file %i\n",pBufferSize);
    return fwrite(pBuffer, pBufferSize, 1, FileOut);

int BUFFERSIZE= 32768;
AVIOContext *pAVIOContext= NULL;
unsigned char *pBufferCallBack= (unsigned char*)av_malloc(BUFFERSIZE *
pAVIOContext= avio_alloc_context(pBufferCallBack, BUFFERSIZE, 1, NULL,
NULL, WritePacket, NULL);

After avformat_write_header I would like to flush that to direct to the
buffer before I write any frames to the buffer.  As of now it takes a 30
frames before that buffer flushes.  I need access to the header before
frames are written.  I tried avio_flush, but that didn't seem to do

Is there a way I can do this?

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