[FFmpeg-devel] [PATCH 1/2] avformat/utils: Assert that stream_index is valid

[Marton Balint]

On Tue, 24 Sep 2019, Gyan wrote:

>
>
> On 24-09-2019 10:01 PM, Andreas Rheinhardt wrote:
>> There is currently an ordinary check for this (which would lead to a
>> memleak), but given that no demuxer should ever return a packet with an
>> invalid stream_index it is more appropriate for this to be an assert.
>>
>> FATE passes with this change.
>>
>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
>> ---
>>   libavformat/utils.c | 6 ++----
>>   1 file changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/libavformat/utils.c b/libavformat/utils.c
>> index 3983a3f4ce..d8ef5fe54c 100644
>> --- a/libavformat/utils.c
>> +++ b/libavformat/utils.c
>> @@ -884,10 +884,8 @@ int ff_read_packet(AVFormatContext *s, AVPacket *pkt)
>>               continue;
>>           }
>> 
>> -        if (pkt->stream_index >= (unsigned)s->nb_streams) {
>> -            av_log(s, AV_LOG_ERROR, "Invalid stream index %d\n", 
> pkt->stream_index);
>> -            continue;
>> -        }
>> +        av_assert0(pkt->stream_index < (unsigned)s->nb_streams &&
>> +                   "Invalid stream index.\n");
>
> The mpegts demuxer can send packets from new streams which appear 
> mid-way. See the check in ffmpeg.c process_input() which discards these 
> packets.

That checks InputFile->nb_streams not AVFormatContext->nb_streams as far 
as I see.

> Whereas the patch will lead to an abort in fftools and other user apps 
> transcoding a live feed.

Are you sure? I think the demuxer always creates a new stream before 
returning a packet, so AVFormatContext->nb_streams should always be 
up-to-date when this code runs.

Regards,
Marton