[FFmpeg-devel] [PATCH] avformat: remove request_probe assert from ff_read_packet

[Hendrik Leppkes]

On Tue, Oct 18, 2016 at 11:26 PM, Andreas Cadhalpun
<andreas.cadhalpun at googlemail.com> wrote:
> On 18.10.2016 22:56, Michael Niedermayer wrote:
>> On Tue, Oct 18, 2016 at 10:31:37PM +0200, Andreas Cadhalpun wrote:
>>> Nothing guarantees to set request_probe to -1, so this assert can be
>>> triggered, e.g. if st->probe_packets is 0.
>>
>> probe_codec() called with NULL should cause
>> st->probe_packets = 0
>> st->request_probe = -1;
>
> Yes, but request_probe can be change to a different value later on,
> e.g. in ff_parse_mpeg2_descriptor:
>
> int ff_read_packet(AVFormatContext *s, AVPacket *pkt)
> {
> [...]
>             if (s->internal->raw_packet_buffer_remaining_size <= 0)
>                 if ((err = probe_codec(s, st, NULL)) < 0) // probe_packets = 0, request_probe = -1
>                     return err;
> [...]
>         ret = s->iformat->read_packet(s, pkt);
> ~~~
> ff_parse_mpeg2_descriptor([...])
> {
> [...]
>     switch (desc_tag) {
> [...]
>     case 0x05: /* registration descriptor */
> [...]
>                 st->request_probe = 50;
> [...]
> }
> ~~~
> [...]
>                 if (st->probe_packets) // still 0
>                     if ((err = probe_codec(s, st, NULL)) < 0)
>                         return err;
>                 av_assert0(st->request_probe <= 0); // now 50
> SIGABRT
>

Can you actually make that happen, or is that just speculation?

- Hendrik