[Libav-user] AVPacket av_malloc av_packet_unref question

[Brian Brice]

You should probably use av_packet_alloc instead of av_malloc on the
AVPacket.  This will ensure that each field is initialized properly.

The demuxer could set the data pointer to its own internal storage
(when buf is NULL) which can be reused when you call av_read_frame
another time.  The call to av_packet_unref is mostly to decrement the
reference count on the buf pointer.  It does other things, like
releasing the side data and resetting the fields to some default.

On Fri, Aug 19, 2016 at 3:31 PM, Charles <linux2 at orion15.org> wrote:
> I have a piece of code that appears to work, that is to say it does stream
> packets..
> It goes like this:
> av_packet = (AVPacket *) av_malloc( sizeof( AVPacket ) );
> while ( 1 ) /// reading in from file out to mpegts
> {
>    av_read_frame( av_in_fmt_ctx, m_avpacket );
> [...]
>    ret = av_interleaved_write_frame( av_out_fmt_ctx, av_packet );
>    av_packet_unref( av_packet );
> }
>
> In the include headers I find this type of verbage ::
>  * The side data is always allocated with av_malloc(), copied by
>  * av_packet_ref() and freed by av_packet_unref().
>
> From reading the av_read_frame I know the packed is a reference to another
> packet (at least the buf).
>
> Question :
> What is av_malloc doing if the packet is getting unref and passed back into
> av_read_frame without another malloc?
>
> Follow Up :
> Is this thread safe?
>
> Thanks
> cco
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-- 
Brian Brice
http://heapify.org/