[Libav-user] AVPacket av_malloc av_packet_unref question

[Charles]

Is there good information somewhere outlining sync between stream and frame?
Like how to handle the 257 in frame that finishes before you make the 256 getFrame call
av_read_frame returns 0 not EAGAIN

Are the contex thread safe, i.e. one ctx one thread...running multiple decode/encode threads?

Thanks
cco


On 08/21/2016 08:45 PM, salsaman wrote:
> Yes. I have found you can also check if pkt->packet.size == 0 instead of pkt->buf == NULL.
>
>
> Regards,
> Gabriel.
>
>
>
>
> http://lives-video.com
> https://www.openhub.net/accounts/salsaman
>
> On Sun, Aug 21, 2016 at 9:36 PM, Charles <linux2 at orion15.org <mailto:linux2 at orion15.org>> wrote:
>
>     On 08/21/2016 07:23 PM, Brian Brice wrote:
>
>         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 <mailto: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?
>
>
>     This may be poor form but I just declared an AVPacket
>
>        /// \note setup stuff used in ReadFrame
>        av_init_packet( &av_pkt );
>        av_pkt.data = NULL;  /// demux will allocate
>        av_pkt.size = 0;
>     [...]
>
>        Comments from av_read_frame
>
>              * If pkt->buf is NULL, then the packet is valid until the next
>              * av_read_frame() or until avformat_close_input(). Otherwise the packet
>              * is valid indefinitely. In both cases the packet must be freed with
>              * av_packet_unref when it is no longer needed.
>
>     I am using the new ABI avcodec_send_packet / avcodec_receive_frame
>     Since it is a spinning thread, the packet stays in scope and I just never delete it...
>     Seems to work ok
>
>
>     Thanks
>     cco
>
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