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• Next pts does not match previous pts plus duration when transcoding an AAC audio with ffmpeg

  17 septembre 2021, par b1sub

  In my understanding, the following statement must hold :

  


  next pts = previous pts + duration


  


  But, I got this list of PTSes from ffprobe that looks odd to me :

  


  <packet pts="63000" duration="2089">&#xA;<packet pts="65070" duration="2089">&#xA;<packet pts="67140" duration="2089">&#xA;<packet pts="69300" duration="2089">&#xA;<packet pts="71370" duration="2089">&#xA;<packet pts="73440" duration="2089">&#xA;<packet pts="75510" duration="2089">&#xA;<packet pts="77670" duration="2089">&#xA;</packet></packet></packet></packet></packet></packet></packet></packet>

  


  The corresponding PTS gaps are as follows. You can see none of the below gaps matches 2089 :

  


  63000 <> 65070: 2070
65070 <> 67140: 2070
67140 <> 69300: 2160
69300 <> 71370: 2070
71370 <> 73440: 2070
73440 <> 75510: 2070
75510 <> 77670: 2160


  


  I have no deep understanding of AAC or transcoding, so I talked with some random guy on #ffmpeg. As per what he said, the gap should be a fixed value :

  


  20:01 -!- Icedream [~icedream@hzn-b.serverkomplex.de] has quit [Quit: A lol made me boom.]
20:02 < DeHackEd> I would expect them to increment at a constant rate, since AAC (which is probably what you're using) uses fixed size
                  audio chunks. But that's very inconsistent
20:03 < DeHackEd> (+/- 1 pts number would be acceptable)


  


  To tell you the truth, this is a problematic video, but not in a way you would expect. I'm getting intermittent audio clipping sound, if two or more audio packets are crammed into a single PES packet. What's special about this configuration is that, the player must guess PTSes for the trailing audio packets except the first one. Since the PTS gaps are not consistent, the player must have used wrong PTSes for the trailing ones, and this looks to me like the cause.

  


  But, what could be the trigger ? Here are some contexts you can kindly refer to :

  


  

  • the original video has no surprising PTS gap. This is the result from my custom-made script to extract all unique gaps :

  


  


  $ ./foo.sh ./original.flv
diff 296448 occurs at 296448 // just a first packet (=has no previous packet)
diff 24 occurs at 296472
diff 23 occurs at 296495


  


  

  • this is the command I used for transcoding :

  


  


  $FFMPEG -hide_banner -loglevel info -nostats \
    -i $input \
    -map "[out1]" -c:v libx264 -r 30 -force_key_frames "expr:gte(t, n_forced*$keyFrameInterval)" -preset veryfast -vprofile high -minrate 4.5M -maxrate 6M -bufsize 6M \
    -map 0:a -c:a aac -b:a:1 128K -af "aformat=sample_rates=44100|48000:channel_layouts=stereo" \
    -map 0:a -c:a aac -b:a:2 32K -af "aformat=sample_rates=44100|48000:channel_layouts=stereo" \
    -f mpegts -tune zerolatency pipe:1 > \
        >($FFMPEG -hide_banner -loglevel info -nostats \
            -i - \
            -map 0:v -c:v copy -map 0:1 -c:a copy -bsf:a aac_adtstoasc -tune zerolatency -f flv -max_muxing_queue_size 1024 ${output}_1080 \
            -map 0:v -s $(width 1280 720 $orientation)x$(height 1280 720 $orientation) -c:v libx264 -r 30 -force_key_frames "expr:gte(t, n_forced*$keyFrameInterval)" -preset veryfast -vprofile high -minrate 3M -maxrate 4M -bufsize 4M -map 0:1 -c:a copy -bsf:a aac_adtstoasc -f flv -tune zerolatency -max_muxing_queue_size 1024 ${output}_720 \
            ...


  


• How to match precompiled static library's debugging symbols to source code with Xcode 5 ?

  21 septembre 2013, par Chris Ballinger

  I have to compile FFmpeg for iOS using an external build script, but when I am debugging I see assembler if I delve too deep into libavformat library functions :

  0x109a73:  cmpl   $0, 1192(%ebp)
  
  0x109a7a:  jns    0x109a86                  ; mov_write_header + 198 at movenc.c:3539
  
  0x109a7c:  movl   $1, 1192(%ebp)
  
  0x109a86:  movl   16(%ebp), %eax
  
  0x109a89:  cmpl   $0, 84(%eax)
  
  0x109a8d:  movl   %edx, %ecx
  
  0x109a8f:  jne    0x109ad9                  ; mov_write_header + 281 at movenc.c:3548
  
  0x109a91:  testb  $2, 48(%ecx)
  
  0x109a95:  jne    0x109ac1                  ; mov_write_header + 257 at movenc.c:3541

  There are clear debugging symbols left behind which would lead me to believe that there should be some way to tell Xcode the location of this source code to allow easier debugging.

  Is this even possible ?

  edit : I found a related question here No symbols/source for external library in Xcode 4

  So when I run xcrun dwarfdump libavformat.a | grep "\.c" I get a bunch of results like this :

  AT_decl_file( "libavformat/movenc.c" )

  So I tried putting the relevant source files in folders relative to both the .a file and my .xcodeproj file, but neither of those methods worked. Full source code is available here : https://github.com/openwatch/livestreamer-ios

  edit2 : I found another question about how to set the source mapping for lldb but I'm not quite sure what to do... LLDB equivalent of gdb "directory" command for specifying source search path ?

  It seems like I might need to do

  (lldb) settings set target.source-map libavformat/movenc.c /path/to/libavformat/movenc.c 

  for every file I need ?

• Input link in1:v0 parameters (size XXX, SAR XXX) do not match the corresponding output link in0:v0 parameters (XXX, SAR 1:1) [duplicate]

  1er mars 2020, par theapache64

  I’ve two files, a mp4 and a mp3 file. I want to add a 3 seconds intro screen with title Welcome and black background to the head of the video with the mp3 as background. So here’s what I wrote.

  ffmpeg \
  
      -i input.mp4 \
  
      -i bgm.mp3 \
  
      -f lavfi -i color=c=black:s="1280"x"544":d=3.0 \
  
      -filter_complex \
  
          "[2:v]
  
    drawtext=
  
      fontsize=30
  
      :fontcolor=white
  
      :x=(w-text_w)/2
  
      :y=(h-text_h)/2
  
      :text='WELCOME',
  
      geq=0:128:128
  
  [introVideo];
  
  
  
  [1:a]
  
      atrim=0.0:3.0
  
  [introAudio];
  
  
  
  [introVideo][introAudio][0:v][0:a]concat=n=2:v=1:a=1" -preset superfast output.mp4

  but am getting below error when I try to execute the command

  [Parsed_concat_3 @ 0x55c02756fa00] Input link in1:v0 parameters (size 1280x544, SAR 1299:1280) do not match the corresponding output link in0:v0 parameters (1280x544, SAR 1:1)
  
  [Parsed_concat_3 @ 0x55c02756fa00] Failed to configure output pad on Parsed_concat_3
  
  Error reinitializing filters!
  
  Failed to inject frame into filter network: Invalid argument
  
  Error while processing the decoded data for stream #0:1
  
  Conversion failed!

  Any help will be highly appreciated.

  PS : I am a beginner in video processing and ffmpeg.