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• H264 NAL unit header - detect type and bring custom videos in this format

  7 décembre 2015, par user3387542

  On a special interface on my device, I can see the NAL units passing by. Two example files shown below :

  P-Frames:
  
  00 00 00 01 41 FC 0F 90 86 DE F9 E1 4D 37 AE D3 
  
  24 A9 F2 F7 E8 A0 9A 9E B3 FD FE 3A D2 77 3E 79 
  
  8C 93 2D 75 61 60 A0 FA BF CB 46 B6 67 A6 C2 81 
  
  2B 47 A5 A2 71 5D 4F 90 32 14 EE D5 DE 58 3B 6E 
  
  ...
  
  
  
  I-Frames / Key-Frames:
  
  00 00 00 01 65 B8 20 67 FF FE 1E 8A 00 02 05 BE 
  
  4D 49 85 EB FC 9E 44 F7 D0 CE A0 77 25 CD 80 D4 
  
  4A A4 E5 66 EE E7 F9 17 E5 81 DC 94 9C 2B 3C DF 
  
  DE D2 63 CC 89 98 82 4D AF C6 BF E8 3F 0D 3C BE 
  
  ...

  My goal is, to be able to overwrite this data in order to inject / play my own video. So fare so good, seems to work but it doesn’t look good yet. While replayed NAL units, which were previously stored from the very same interface look good, an injected video doesn’t. I think i did not get the right video format yet.
  I used different tools like ffmpeg to convert videos into a h264 format. But the video still never looks fine. I think the issue is with the key-frames. While I see lots of 00 00 00 01 41 parts in the converted videos, i can’t find a 00 00 00 01 65.

  What kind of video format is this ? And how to convert my own videos into this format ? By using ffmpeg or other tools.

  Thanks in advance

• aacenc_tns : tune and reduce artifacts

  6 décembre 2015, par Rostislav Pehlivanov

  aacenc_tns : tune and reduce artifacts
  There are a couple of major changes here :
  1. Start using TNS coefficient compression.
  
  2. Start using 3 bits per coefficient maximum for short windows.
  
  The bits we save from these 2 changes seem to make a nice impact on the
  
  rest of the file/windows.
  3. Remove special case gain checking for short windows.
  
  4. Modify the coefficient loop to support up to 3 windows.
  
  The additional restrictions on TNS were something that was no in the
  
  specifications and furthermore restricting TNS to only low energy short
  
  windows was done to compensate for bugs elsewhere in the code.
  Overall, the improvements here reduce crackling artifacts heard in very
  
  noisy tracks.
  Signed-off-by : Rostislav Pehlivanov <atomnuker@gmail.com>
  

  • [DH] libavcodec/aacenc_tns.c

• Quickly check the integrity of video files inside a directory with ffmpeg

  4 février 2017, par DMT

  I’m desperately searching for a convenient method to check the integrity of .mp4 files inside a specific directory with folders in it. Both the names of the .mp4 files and the folders contain spaces, special characters and numbers.

  I’ve already found a proper ffmpeg command to quickly identify a damaged .mp4 file, taken from here :
  ffmpeg -v error -i filename.mp4 -map 0:1 -f null - 2>error.log

  If the created error.log contains some entries, then the file is obviously corrupted. The opposite would be an empty error.log.

  The next step would be to apply this command to every .mp4 file within the folder and its subfolders. Some guides, like here and here, do describe how to apply a ffmpeg command recursively, but my coding skills are limited, so therefore I can’t find a way to combine these commands to get the following :

  A way to test all .mp4 files inside a folder (recursively) with the aforementioned ffmpeg command, that should create .log files, only if a video file does contain errors (read has some content) and it should inherit the name of the broken file, to know which file is corrupted.

  Using Ubuntu Gnome 15.10.