[Libav-user] How To Duplicate AVPacket

[Xiemin Chen]

Dear nfxjfg:
    Seems it's still not all right for the solution which you mentioned.
    I write the codes like following:
        1. pPacket  = av_malloc(sizeof(AVPacket))
        2. av_init_packet(pPacket);
        3. av_read_frame(pPacket);
        4. put_queue(packet);

    But it seems for a little situation, the frame will contain garbage.
About 0.5s per 30 seconds I can reproduce this issue.
    Is there another way I can improve my code?
    Thanks very much.

Sincerely



2014-06-26 9:17 GMT-04:00 Xiemin Chen <chenxiemin at gmail.com>:

> Dear nfxjfg:
>     I just do av_malloc(sizeof(AVPacket)) instead of define local variable
> AVPacket packet before av_read_frame().
>     And nothing else except for putting into queue, then seems that it
> does solve my problem. Thanks for your professional answer.
>     Also thanks for indicating my potential memory-leaking mistake.
>     Thanks very much.
>
> Sincerely
>
>
>
> 2014-06-26 8:33 GMT-04:00 wm4 <nfxjfg at googlemail.com>:
>
> On Wed, 25 Jun 2014 20:46:59 -0400
>> Xiemin Chen <chenxiemin at gmail.com> wrote:
>>
>> > Dear all:
>> >     I want to split av_read_frame() and avcodec_decode_video2() in to
>> > different thread so I need to put a queue behind them. av_read_frame()
>> read
>> > a packet then put the packet into queue, avcodec_decode_video2() read a
>> > packet from the queue then decode.
>> >     But sometimes the decoded frames may contain rubbish, it's random.
>> So I
>> > think that AVPacket shares its data memory and overwrite by somebody
>> before
>> > I decode it. The following code like this:
>>
>> Why do you think that? It could be something else. Did you test with
>> valgrind?
>>
>> >          1. av_read_frame(&packet);
>> >          2.     av_dup_packet(&packet);
>> >          3.     AVPacket *newPakcet = av_malloc(sizeof(AVPacket));
>> >          4.     *newPacket = packet;
>>
>> It depends what you do with the original packet after this. If you
>> unref it, the packet might be free'd. If you malloc the AVPacket before
>> the av_read_frame call, and then put that into the queue, you should be
>> fine.
>>
>> >          5.  put_queue(packet);
>> >          6.  get_queue(&packet); (Another thread)
>> >          7.  avcodec_decode_video2(packet, &frame);
>> >          8.  show frame;
>> >     Is there any mistake I took on these codes? Thanks very much.
>> >
>> > Sincerely
>>
>> AVPackets have other data than the packet buffer - at least side data.
>> av_dup_packet() is an old API that AFAIK does nothing on packets
>> returned by libavformat. (Yes, that is very misleading - and I'm not
>> even sure if it _really_ does nothing.) Now you should use
>> av_packet_ref(), which is a relatively recently added function. But
>> it looks like you don't need it in your specific use-case.
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>>
>
>
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