[FFmpeg-devel] [PATCH] dashenc: check pts to prevent division by zero error

[Alfred E. Heggestad]

On 31/01/2020 14:17, James Almer wrote:
> On 1/31/2020 10:08 AM, Jeyapal, Karthick wrote:
>>
>> On 1/30/20 3:28 PM, Alfred E. Heggestad wrote:
>>> this usecase will cause a division by zero trap:
>>>
>>> 1. dashenc has received one frame
>>> 2. os->max_pts and os->start_pts have same value
>>> 3. delta between max_pts and start_pts is 0
>>> 4. av_rescale_q(0, x, y) returns 0
>>> 5. this value is used as denominator in division
>>> 6. Bang! -> segfault
>>>
>>> this fix checks that max_pts > start_pts.
>>> the fix has been tested and works.
>>>
>>> please review and suggest better fixes.
>>>
>>> Signed-off-by: Alfred E. Heggestad <alfred.heggestad at gmail.com>
>>> ---
>>>    libavformat/dashenc.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/libavformat/dashenc.c b/libavformat/dashenc.c
>>> index f555f208a7..3b651b9514 100644
>>> --- a/libavformat/dashenc.c
>>> +++ b/libavformat/dashenc.c
>>> @@ -1883,7 +1883,7 @@ static int dash_flush(AVFormatContext *s, int
>>> final, int stream)
>>>   
>>> st->time_base,
>>>   
>>> AV_TIME_BASE_Q));
>>>
>>> -        if (!os->muxer_overhead)
>>> +        if (!os->muxer_overhead && os->max_pts > os->start_pts)
>>>                os->muxer_overhead = ((int64_t) (range_length -
>>> os->total_pkt_size) *
>>>                                      8 * AV_TIME_BASE) /
>>>                                     av_rescale_q(os->max_pts - os->start_pts,
>> LGTM.
>>
>> This actually exposes a corner case bug in overhead calculation logic.
>> Guess we will need to come up with a better logic for it.
>> Until then, this fix will atleast make sure things don’t crash.
>>
>> Thanks,
>> Karthick
> 
> Applied.

Great!

Thanks Jeyapal and James.



/alfred