[FFmpeg-devel] [PATCH v2] ffmpeg: allow full range of dts_delta_threshold

[Gyan Doshi]

On 15-04-2020 01:33 am, Michael Niedermayer wrote:
> On Tue, Apr 14, 2020 at 02:48:47PM +0530, Gyan Doshi wrote:
>> For inputs from demuxers with AVFMT_TS_DISCONT flag,
>> the existing condition,
>>
>>    delta < -1LL*dts_delta_threshold*AV_TIME_BASE
>>
>> is rendered superflous due to the fixed threshold in
>>
>> pkt_dts + AV_TIME_BASE/10 < FFMAX(ist->pts, ist->dts)
>>
>> This prevents users from setting a high threshold to
>> avoid discontinuity correction due to errant timestamps.
>>
>> Now, the maximum of the two thresholds is used.
>>
>> fate-mpeg4-resolution-change call changed to preserve existing
>> timestamp correction by ffmpeg.c
>> ---
>> Tested with multiple satellite MPEG-TS inputs.
>>
>>   fftools/ffmpeg.c     | 2 +-
>>   tests/fate/mpeg4.mak | 2 +-
>>   2 files changed, 2 insertions(+), 2 deletions(-)
> breaks:
> ./ffmpeg -i 'concat:angels.mpg|angels.mpg'  -vsync 0  file.avi
>
> ...
> frame=   24 fps=0.0 q=12.5 Lsize=     215kB time=00:00:07.50 bitrate= 234.7kbits/s speed=75.5x
> video:84kB audio:110kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 10.697786%
>
> vs.
>
> ...
> [avi @ 0x5601caccc180] Non-monotonous DTS in output stream 0:1; previous: 219, current: 86; changing to 220. This may result in incorrect timestamps in the output file.
> [avi @ 0x5601caccc180] Non-monotonous DTS in output stream 0:1; previous: 220, current: 87; changing to 221. This may result in incorrect timestamps in the output file.
> [avi @ 0x5601caccc180] Non-monotonous DTS in output stream 0:1; previous: 221, current: 88; changing to 222. This may result in incorrect timestamps in the output file.
> [avi @ 0x5601caccc180] Non-monotonous DTS in output stream 0:1; previous: 222, current: 89; changing to 223. This may result in incorrect timestamps in the output file.
> [avi @ 0x5601caccc180] Non-monotonous DTS in output stream 0:1; previous: 223, current: 90; changing to 224. This may result in incorrect timestamps in the output file.
> [avi @ 0x5601caccc180] Non-monotonous DTS in output stream 0:1; previous: 224, current: 91; changing to 225. This may result in incorrect timestamps in the output file.
> [mpeg4 @ 0x5601cac87540] Invalid pts (72) <= last (83)
> Video encoding failed

Yes, if the input includes a mid-stream dts reset of gap less than the 
default value of dts_delta_threshold then timestamps won't be made 
continuous. Default value is 10 seconds but till now it wasn't enforced 
for negative jumps, so your command worked. With this change, user will 
have to set it manually if they expect smaller jumps.

What can be done is to set the default value to 0, and then set separate 
values for positive and negative jumps inside the block to keep current 
behaviour. If user-set to non-zero, then the user's value is honoured.

Gyan