[FFmpeg-devel] [PATCH] avfilter/f_cue: add cue and acue filters

[Marton Balint]

On Sat, 1 Sep 2018, Bodecs Bela wrote:

> Hi Balint,
>
>
> 2018.08.25. 20:35 keltezéssel, Marton Balint írta:
>> To delay filtering until a given wallclock timestamp.
>>
>> Signed-off-by: Marton Balint <cus at passwd.hu>
>> ---
>>   doc/filters.texi         |  36 ++++++++++
>>   libavfilter/Makefile     |   2 +
>>   libavfilter/allfilters.c |   2 +
>>   libavfilter/f_cue.c      | 182 +++++++++++++++++++++++++++++++++++++++++++++++
>>   libavfilter/version.h    |   2 +-
>>   5 files changed, 223 insertions(+), 1 deletion(-)
>>   create mode 100644 libavfilter/f_cue.c
>>
>> diff --git a/doc/filters.texi b/doc/filters.texi
>> index 32c95b591c..79eec0c808 100644
>> --- a/doc/filters.texi
>> +++ b/doc/filters.texi
>> @@ -551,6 +551,11 @@ Set LFO range.
>>   Set LFO rate.
>>   @end table
>> 
>> + at section acue
>> +
>> +Delay audio filtering until a given wallclock timestamp. See the @ref{cue}
>> +filter.
>> +
>>   @section adeclick
>>   Remove impulsive noise from input audio.
>> 
>> @@ -6987,6 +6992,37 @@ indicates 'never reset', and returns the largest area encountered during
>>   playback.
>>   @end table
>> 
>> + at anchor{cue}
>> + at section cue
>> +
>> +Delay video filtering until a given wallclock timestamp. The filter first
>> +passes on @option{preroll} amount of frames, then it buffers at most
>> + at option{buffer} amount of frames and waits for the cue. After reaching the cue
>> +it forwards the buffered frames and also any subsequent frames coming in its
>> +input.
>> +
>> +The filter can be used synchronize the output of multiple ffmpeg processes for
>> +realtime output devices like decklink. By putting the delay in the filtering
>> +chain and pre-buffering frames the process can pass on data to output almost
>> +immediately after the target wallclock timestamp is reached.
>> +
>> +Perfect frame accuracy cannot be guaranteed, but the result is good enough for
>> +some use cases.

> just for my curiousity, will you please give an example/use_case how to 
> use these filters?

Here is a shell script:

#!/bin/bash
UNIX_TIMESTAMP=`date +%s`
TS=$((UNIX_TIMESTAMP*1000000 + 2500000))
ffmpeg -nostdin -nostats -stream_loop -1 -i input1.mp4 \
  -vf "format=uyvy422,cue=$TS:preroll=0.5:buffer=0.5" \
  -af "acue=$TS:preroll=0.5:buffer=0.5" -f decklink "DeckLink Duo (1)" &
ffmpeg -nostdin -nostats -stream_loop -1 -i input2.mp4 \
  -vf "format=uyvy422,cue=$TS:preroll=0.5:buffer=0.5" \
  -af "acue=$TS:preroll=0.5:buffer=0.5" -f decklink "DeckLink Duo (2)" &
ffmpeg -nostdin -nostats -stream_loop -1 -i input3.mp4 \
  -vf "format=uyvy422,cue=$TS:preroll=0.5:buffer=0.5" \
  -af "acue=$TS:preroll=0.5:buffer=0.5" -f decklink "DeckLink Duo (3)" &
ffmpeg -nostdin -nostats -stream_loop -1 -i input4.mp4 \
  -vf "format=uyvy422,cue=$TS:preroll=0.5:buffer=0.5" \
  -af "acue=$TS:preroll=0.5:buffer=0.5" -f decklink "DeckLink Duo (4)" &

We are doing something similar to drive 16 TVs in a studio set 
simultaneously.

Regards,
Marton