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• avcodec/h26[45]_metadata_bsf : Use separate contexts for reading/writing

  6 juillet 2020, par Andreas Rheinhardt

  avcodec/h26[45]_metadata_bsf : Use separate contexts for reading/writing
  Currently, both bsfs used the same CodedBitstreamContext for reading and
  
  writing ; as a consequence, the state of the writer's context at the
  
  beginning of writing a fragment is exactly the state of the reader after
  
  having read the fragment ; in particular, the writer might not have
  
  encountered one of its active parameter sets yet.
  This is not nice and may lead to invalid output even when the input
  
  is completely spec-compliant : Think of an access unit containing
  
  a primary coded picture referencing a PPS with id id (that is known from
  
  an earlier access unit/from extradata), then a new version of the PPS
  
  with id id and then a redundant coded picture that is also referencing
  
  the PPS with id id. This is spec-compliant, as the standard allows to
  
  overwrite a PPS with a different PPS in between coded pictures and not
  
  only at the beginning of an access unit. In this scenario, the reader
  
  would read the primary coded picture with the old PPS and the redundant
  
  coded picture with the new PPS (as it should) ; yet the writer would
  
  write both with the new PPS as extradata which might lead to errors or
  
  to invalid data being output without any error (e.g. if the two PPS
  
  differed in redundant_pic_cnt_present_flag).
  The above scenario does not directly translate to HEVC as long as one
  
  restricts oneself to input with nuh_layer_id == 0 only (as cbs_h265
  
  does : it currently strips away any NAL unit with nuh_layer_id > 0 when
  
  decomposing) ; if one doesn't the same issue as above can happen.
  If one also allowed input packets to contain more than one access unit,
  
  issues like the above can happen even without redundant coded
  
  pictures/multiple layers.
  Therefore this commit uses separate contexts for reader and writer.
  Reviewed-by : Mark Thompson <sw@jkqxz.net>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavcodec/h264_metadata_bsf.c
  • [DH] libavcodec/h265_metadata_bsf.c

• Splitting m4a into multiple files with ffmpeg

  16 juillet 2020, par ARuiz

  I have an audio file (.m4a) and want to split it into smaller pieces using ffmpeg. All answers I have seen do something along one of the following two possibilities :

  


  

  1. ffmpeg -i inputFile -map 0 -f segment -segment_time 60 -c copy "$output%03d.m4a

  


  


  or

  


  

  2. ffmpeg -i inputFile -acodec copy -ss start_time -to end_time outputFile

  


  


  With 1. the first file is fine. From the second file on, I just get a minute of silence in quicktime, and in VLC the file plays but the timing is odd : for example the second file should have second 0 equals to second 60 in the original file. However in vlc it starts playing on second 60 and goes on to second 120.

  


  With 2. I have to set start times and end for each file, unfortunately I notice a small jump when I play one after the other, so it seems as if some miliseconds are lost.

  


  There are definitely a few old questions asked around this, but none of them actually helped me with this.

  


• FFMPEG — Error when trying to concat multiple files with and without audio

  7 août 2020, par Philban

  Ok so thanks to a fellow user I have the following FFMPEG command that concats 4 videos together. Now if I use this command with 4 video files that all have audio everything works ! However, if 1 or more of the videos do not have sound I get a "matches no streams" error.

  


  Can someone spot whats wrong here please ?

  


  Video Input 1 - No Audio so adding the anullsrc
Video 2 - Has Audio
Video 3 - No Audio
Video 4 - Has Audio

  


  ffmpeg -i noSound1.mp4 -i story1.mp4 -i noSound2.mp4 -i story2.mp4 -t 0.1 -f lavfi -i anullsrc=channel_layout=stereo -filter_complex 
"[0:v]scale=1280:720:force_original_aspect_ratio=decrease,pad=1280:720:(ow-iw)/2:(oh-ih)/2,setsar=1,fps=30,format=yuv420p[v0]; 
 [1:v]scale=1280:720:force_original_aspect_ratio=decrease,pad=1280:720:(ow-iw)/2:(oh-ih)/2,setsar=1,fps=30,format=yuv420p[v1]; 
 [2:v]scale=1280:720:force_original_aspect_ratio=decrease,pad=1280:720:(ow-iw)/2:(oh-ih)/2,setsar=1,fps=30,format=yuv420p[v2]; 
 [3:v]scale=1280:720:force_original_aspect_ratio=decrease,pad=1280:720:(ow-iw)/2:(oh-ih)/2,setsar=1,fps=30,format=yuv420p[v3]; 
 [0:a]aformat=sample_rates=48000:channel_layouts=stereo[a0]; 
 [1:a]aformat=sample_rates=48000:channel_layouts=stereo[a1]; 
 [2:a]aformat=sample_rates=48000:channel_layouts=stereo[a2]; 
 [3:a]aformat=sample_rates=48000:channel_layouts=stereo[a3]; 
 [v0][a0][v1][a1][v2][a2][v3][a3]concat=n=4:v=1:a=1[v][a]" 
-map "[v]" -map "[a]" -c:v libx264 -c:a aac -movflags +faststart testOutput.mp4


  


  Here is the error :

  


  Stream specifier ':a' in filtergraph description [0:v]scale=1280:720:force_original_aspect_ratio=decrease,pad=1280:720:(ow-iw)/2:(oh-ih)/2,setsar=1,fps=30,format=yuv420p[v0];  [1:v]scale=1280:720:force_original_aspect_ratio=decrease,pad=1280:720:(ow-iw)/2:(oh-ih)/2,setsar=1,fps=30,format=yuv420p[v1];  [2:v]scale=1280:720:force_original_aspect_ratio=decrease,pad=1280:720:(ow-iw)/2:(oh-ih)/2,setsar=1,fps=30,format=yuv420p[v2];  [3:v]scale=1280:720:force_original_aspect_ratio=decrease,pad=1280:720:(ow-iw)/2:(oh-ih)/2,setsar=1,fps=30,format=yuv420p[v3];  [0:a]aformat=sample_rates=48000:channel_layouts=stereo[a0];  [1:a]aformat=sample_rates=48000:channel_layouts=stereo[a1];  [2:a]aformat=sample_rates=48000:channel_layouts=stereo[a2];  [3:a]aformat=sample_rates=48000:channel_layouts=stereo[a3];  [v0][a0][v1][a1][v2][a2][v3][a3]concat=n=4:v=1:a=1[v][a] matches no streams.


  


  Now a slightly separate question. If I have N input videos where i do not know if they have sound or not, is there a way I can have a loop that does the above without having massive amounts of command lines ?
Many thanks !