[FFmpeg-devel] [PATCH 1/2] avcodec/h264_ps: Check for truncation at fixed_frame_rate_flag

[James Almer]

On 12/15/2019 9:03 PM, Carl Eugen Hoyos wrote:
> Am Mo., 16. Dez. 2019 um 01:00 Uhr schrieb James Almer <jamrial at gmail.com>:
>>
>> On 12/15/2019 8:50 PM, Carl Eugen Hoyos wrote:
>>> Am So., 15. Dez. 2019 um 23:25 Uhr schrieb James Almer <jamrial at gmail.com>:
>>>>
>>>> On 12/15/2019 7:00 PM, Michael Niedermayer wrote:
>>>>> Fixes: Ticket7249 (No longer displaying a scary red message)
>>>>>
>>>>> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
>>>>> ---
>>>>>  libavcodec/h264_ps.c | 4 ++++
>>>>>  1 file changed, 4 insertions(+)
>>>>>
>>>>> diff --git a/libavcodec/h264_ps.c b/libavcodec/h264_ps.c
>>>>> index e8738d8502..74f12f8979 100644
>>>>> --- a/libavcodec/h264_ps.c
>>>>> +++ b/libavcodec/h264_ps.c
>>>>> @@ -203,6 +203,10 @@ static inline int decode_vui_parameters(GetBitContext *gb, AVCodecContext *avctx
>>>>>              sps->num_units_in_tick = num_units_in_tick;
>>>>>              sps->time_scale = time_scale;
>>>>>          }
>>>>> +        if (get_bits_left(gb) == 0) {
>>>>
>>>> Doing this check here sounds like it's tailored specifically for the
>>>> sample in the ticket. What if another file is truncated one bit after
>>>> this point? Or one bit before? You will get the scary red message for
>>>> it. Will you also add a check for it?
>>>> We can't clutter this file with new get_bits_left() checks every time a
>>>> user shares their broken samples with us just to get a less scary output
>>>> in their terminals.
>>>
>>> Do you know of another proprietary or open-source encoder that encodes
>>> streams with such a truncation?
>>
>> There was an old hevc encoder that did something like that. We ended up
>> adding a workaround for it as well.
> 
>> And i can imagine capturing a
>> transport stream with bad network conditions could result in all kinds
>> randomly placed truncation.
> 
> I don't think a "random" truncation as produced by reception or
> network issues can lead to similar messages as in the ticket.

Can you elaborate why? If a sample stored in some container is truncated
in the VUI one bit after this point, will it not still print the
overread error level log message?

> 
> Carl Eugen
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