[FFmpeg-user] streamselect in a realtime application
ffmpeg at gyani.pro
Thu Jun 16 10:53:13 EEST 2022
On 2022-06-16 01:17 pm, Michael Koch wrote:
> Am 16.06.2022 um 09:33 schrieb Gyan Doshi:
>> On 2022-06-16 12:45 pm, Michael Koch wrote:
>>> I would like to understand why in some cases -loop 1 is required
>>> before the input files, and in some cases it can be omitted.
>> -loop option is specific to the image sequence demuxer. Without it, a
>> single image input is a video stream of 1 frame length.
> But why does this example work without -loop 1? Is it an undocumented
> feature of the remap filter, that it keeps the last mapping file alive?
> ffmpeg -i in.mp4 -i xmap.pgm -i ymap.pgm -lavfi remap out.mp4
remap uses framesync which by default, repeats last frame of secondary
input if primary input is still alive.
>> You would apply loop when you need to keep alive an image sequence
>> input at a timestamp beyond its natural length, usually a fade.
>> With the tpad or loop filters, this can be done inside a filtergraph
>> instead of at the demuxer level.
> Which method is better, -loop 1 before the input file, or doing it in
> the filtergraph?
For single image input, filter looping is better as it avoids file I/O
and repeat decoding of the input.
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