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• How the ffmpeg is fixing Handle page termination with same page number ...? [closed]

  11 avril 2024, par adarsh

  Im working on the teletext subtitle feature and faced with subs not clearing issue.
the subtitle lines remain displayed until being replaced by a new version of the specific line. So the subtitles never disappear and often an old line is still displayed, after another, more recent line is displayed/updated.
take a look at the issue in this sample video file : https://code.videolan.org/videolan/vlc/uploads/58c2e1660e94e2df5e8cdb75edf531d9/GODFATHER__03_.ts
Issue reported : https://sourceforge.net/p/zapping/bugs/203/

  


  The player is using ffmpeg and libzvbi library.

  


  At first I suspected that the Erase Page Flag (C4) in the Page Header was not set, but the flag was indeed set (at least once between two LOPs with subtitles). After further debugging it turned out that the Teletext service in the two issues consists of just a single Teletext page - which is the reason here :

  


  The Teletext spec defines the Magazine Serial Flag (C11) in Table 2 (ETSI EN 300 706 v1.2.1) as (bold font by me) :

  


  When set to '1' the service is designated to be in Serial mode and the transmission of a page is terminated by the next page header with a different page number.
When set to '0' the service is designated to be in Parallel mode and the transmission of a page is terminated by the next page header with a different page number but the same magazine number.
The same setting shall be used for all page headers in the service.
(BTW it doesn't really matter, but in these two cases this flag is always 0)

  


  In vbi_decode_teletext in /src/packet.c, storing the page is aborted, if the condition "page terminated" in the C11 definition is not met. But as the service here consists of only one page, this condition is never met !

  


  Luckily, this issue was fixed in ffmpeg- https://github.com/FFmpeg/FFmpeg/commit/b1e0e216462a989a39e7b413aef6d32f8cedc154

  


  and also in zvbi :
https://github.com/zapping-vbi/zvbi/commit/40a6ab0200c46b67b059b5b1fb15793ce780892a

  


  I understand the root cause and fix in zvbi library, and how it is ignoring c4 flag in case the same page no.

  


  But i want to understand how the ffmpeg fix is working ?
ffmpeg fix : https://github.com/FFmpeg/FFmpeg/commit/b1e0e216462a989a39e7b413aef6d32f8cedc154

  


  what is the rule for repeated page headers ?

  


• How to use -filter_complex and -vf together in ffmpeg ?

  11 juillet 2021, par ChhengRavy

  I want to use -filter_complex and -vf together in one line but I can't do that and get error.

  


  First code :

  


  ffmpeg -i 1.mp4 -filter_complex "[0:v]setpts=0.87*PTS[v];[0:a]atempo=1.15[a]" -map "[v]" -map "[a]" e1.mp4


  


  Second code :

  


  ffmpeg -i 1.mp4 -vf "scale=1280:720:force_original_aspect_ratio=decrease,pad=1280:720:-1:-1:color=black" e1.mp4


  


  So I combine two code above together. Combined code :

  


  ffmpeg -i 1.mp4 -filter_complex "[0:v]setpts=0.87*PTS[v];[0:a]atempo=1.15[a]" -map "[v]" -map "[a]" -vf "scale=1280:720:force_original_aspect_ratio=decrease,pad=1280:720:-1:-1:color=black" e1.mp4


  


  I can can't run code I get the error :

  


  -vf/-af/-filter and -filter_complex cannot be used together for the same stream.


  


• FFMpeg concatenation with large list of inputs — how to minimize command line length

  27 août 2020, par huitlacoche

  I have a python tool that concatentates several mp4s together into a single movie file using FFMPEG run from a subprocess call. The issue is that an arbitrarily large number of inputs in the command string will hit the windows CLI character max.

  


  ffmpeg -y -i a.mp4 -i b.mp4 -i c.mp4 -f lavfi -t 0.1 -i anullsrc  -filter_complex '[0]scale=1920:1080:force_original_aspect_ratio=decrease,pad=1920:1080:(ow-iw)/2: (oh- ih)/2,setsar=1[0:v];[1]scale=1920:1080:force_original_aspect_ratio=decrease,pad=1920:1080:(owiw)/2:(oh-ih)/2,setsar=1[1:v];[2]scale=1920:1080:force_original_aspect_ratio=decrease,pad=1920:1080:(ow- iw)/2:(oh-ih)/2,setsar=1[2:v]; [0:v][3:a][1:v][3:a][2:v][3:a]concat=n=3:v=1:a=1[v][a]' -c:v libx264 -map [v] -map [a] output.mp4

  


  Assuming 3 input movies that may or may have audio (hence the null audio source).
This works fine assuming there are no more than 30-50 input files. Often the input files have rather long filepaths and can get long very quickly.

  


  After doing a bit of reading I tried a simple :

  


  ffmpeg -f concat -i files.txt -c copy output.mp4

  


  Which works if I can guarantee that all the files are the same codec/resolution/etc, but this cannot be guaranteed.
I'm not clear on how to translate my filter_complex to work with a text file of inputs. Finding a specific enough solution has proven elusive.

  


  I'd be perfectly fine assigning the input paths to a temporary environment variable but in my use case this doesn't seem to work either. The subprocess call doesn't seem to translate wildcard %MYVAR% calls to environment variables.

  


  I feel like there has to be an answer to this problem. If anyone can suggest a solution I would greatly appreciate it.

  


  Thanks !