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• A 'clean' way to cut an MP4 movie into two sections using FFMPEG ?

  30 août 2020, par Peter in Japan

  I am attempting to use FFMPEG to make a script that can easily split a short MP4 movie with sound into two pieces at a certain point. I've searched through what feels like hundreds of posts to try to find "the" answer, but most of my attempts end up with poor results, broken video files that cause my video play to freeze, and so on. I am attempting to make a script that allows me to easily cut a short anime movie (something grabbed from Twitter or some other short source) and cut it into two sections, so it can be under the 2:20 Twitter time limit, or to cut out some scene I don't want to show my followers.

  


  The issue is that FFMPEG is good at cutting videos into segments, but bad at know where keyframes are, so most videos have two seconds of blank video at the front before some keyframe appears, which looks terrible.

  


  One example I found that works well is below, which cuts any mp4 into a bunch of chunks of n second size (six seconds in the example below). Source and documentation for this is https://moe.vg/3b8eNTs

  


  ffmpeg -i seitokai.mp4 -c:v libx264 -crf 22 -map 0 -segment_time 6 -reset_timestamps 1 -g 30 -sc_threshold 0 -force_key_frames "expr:gte(t,n_forced*1)" -f segment output%03d.mp4

  


  This code works great, at least allowing me to access the "left" side of a video that I want, in this case a six-second segment I want. Can anyone tell me how to accomplish the above, but starting at the 13-second period in said video, so I could get right "right" (not starting from 00:00:00) video cut cleanly ?

  


  Alternately, a single, unified and elegant way to split (re-encode) an MP4 into two segments that forces keyframes from the very beginning of the cut pieces would be wonderful. I can't believe how hard this seems to be.

  


  Thanks in advance for any help you can give ! Greetings from rural Japan !

  


• convert mp4 to hls but with variable segments size

  22 mai 2020, par Pavel Angel Mendoza Villafane

  I saw several examples to change mp4 container to hls using ffmpeg easily with something like this :

  



  ffmpeg -i input.mp4 -profile:v baseline -level 3.0 -s 640x360 -start_number 0 -hls_time 10 -hls_list_size 0 -f hls index.m3u8


  



  I observed that usually the last fragment could be really different with the others (because it is like an offset only). Then I guess that a fix segment length is not mandatory

  



  I have been asking, is it possible to change the size of another fragments ? For example, fix hls_time=10 for all the segments except for segments (1) or (1, 2) such that the length for these to be 5 instead of 10 ?

  



  Is possible ? with ffmpeg or any other ?

  


• Zoom custom ringtones

  9 juillet 2021, par Ferenc Kovács

  I want to add a custom ringtone to Zoom (not implemented in the desktop clients). Did some digging around :

  


  

  • I see the delivered PCM binary files have a SILK_V3 encoding header (bin\ringtone\ringtone.xml).

  


  • So in theory I could create a pcm audio file with Audacity or ffmpeg from wav/mp3

  


  • then encode the raw audio with the Skype SILK SDK

  


  • add the ringtone file to ringtone.xml and localization.xml with a new ID

  


  • reboot Zoom : I should have a new ringtone

  


  


  I have no luck guessing the ringtone parameters (channels, sampling bits, endianness, frequency, etc.)
Maybe someone on SO knows the details on the used format.
Tried to decode say Zoom\bin\ringtones\Ukulele.pcm with silk_v3_decoder from GitHub, but no luck for me, I get 960 x SOH char garbage output.