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Sur d’autres sites (6899)

  • Video files recorded in Google Chrome have stuttering audio

    4 juin 2018, par maxpaj

    Background

    I’m developing a platform where users can record videos of themselves or their screen and send them as video messages to customers / clients.

    I have limited users to only using my application with Google Chrome and I’m using the MediaRecorder API to record the video data from the users screen or webcamera. The codecs that are used for recording are VP8/OPUS (WEBM container).

    I need the videos to run in as many browsers as possible, so I’m using a 3rd party service to transcode videos from whatever format I’m getting from the users to a H.265/AAC MP4 container (caniuse MPEG-4/H.264).

    Issue

    Lately I’ve seen that some videos recorded on Mac OSX machines have the video and audio out of sync or that the video and audio stutters, depending on which player I’m using. I call these video files corrupt, for lack of a better word. Playing a corrupt file in Google Chrome renders smooth playing audio. Playing the video in VLC on my Windows machine renders stuttering audio.

    When I run the corrupt video files through the transcoding service I get video files with stuttering audio, no matter which player I’m using.

    This is an unwanted result and pretty much unacceptable since the audio needs to be smooth in order for the recipient of a video to not be bothered with the quality.

    Debugging

    According to the transcoding service support, this happens because of their mechanisms that try to sync up the audio and video from the corrupt file :

    Inspecting our encoding logs, I’ve noticed the following kind of
    warnings :

    [2018-05-16 14:08:38.009] [pcm_s16le @ 0x1d608c0] pcm_encode_frame :
    filling in for 5856 missing samples (122 ms) before pts 40800 to
    correct sync ! [2018-05-16 14:08:38.009] [pcm_s16le @ 0x1d608c0]
    pcm_encode_frame : dropping 2880 samples (60 ms) at pts 43392 to help
    correct sync to -3168 samples (-66 ms) !

    The problem here comes from the way that the audio in the original
    source file is encoded.

    -

    you should ensure that the audio is not out of sync (audio timestamps
    are correct) in your source file before submitting the job

    Running a corrupt file through ffmpeg on my own machine, re-encoding with the same codecs, produces the same kind of stuttering video. The logs produce an alarming amount of errors. Here is a sample of the log output :

    [libopus @ 0000029938e24d80] Queue input is backward in timeitrate= 194.8kbits/s dup=0 drop=5 speed=0.31x
    
[webm @ 0000029938e09b00] Non-monotonous DTS in output stream 0:1; previous: 15434, current: 15394; changing to 15434. This may result in incorrect timestamps in the output file.
    
[webm @ 0000029938e09b00] Non-monotonous DTS in output stream 0:1; previous: 15434, current: 15414; changing to 15434. This may result in incorrect timestamps in the output file.
    
[libopus @ 0000029938e24d80] Queue input is backward in timeitrate= 193.3kbits/s dup=0 drop=5 speed=0.309x
    
[webm @ 0000029938e09b00] Non-monotonous DTS in output stream 0:1; previous: 15539, current: 15499; changing to 15539. This may result in incorrect timestamps in the output file.
    
[webm @ 0000029938e09b00] Non-monotonous DTS in output stream 0:1; previous: 15539, current: 15519; changing to 15539. This may result in incorrect timestamps in the output file.
    
[libopus @ 0000029938e24d80] Queue input is backward in timeitrate= 192.0kbits/s dup=0 drop=5 speed=0.308x
    
[webm @ 0000029938e09b00] Non-monotonous DTS in output stream 0:1; previous: 15667, current: 15627; changing to 15667. This may result in incorrect timestamps in the output file.
    
[webm @ 0000029938e09b00] Non-monotonous DTS in output stream 0:1; previous: 15667, current: 15647; changing to 15667. This may result in incorrect timestamps in the output file.
    
[libopus @ 0000029938e24d80] Queue input is backward in time

    I tried running the same inputs through another transcoding service and those outputs worked a lot better - video was still stuttering but the audio played smoothly, which is more important to the use case of my application.

    To my knowledge, this have so far only occurred for users on Mac OSX machines.

    Questions

    1. Is there anything I can do to have the files work better ? Or is this entirely a consequence of how encoding of video and audio in Google Chrome works ?

    2. One step in the right direction would be to just be able to detect when the video is corrupt. How can I do that ?

  • Evolution #3560 (Fermé) : Supprimer l’option expérimentale Google Closure Compiler

    4 mai 2017

    Fait en 3.2 par https://zone.spip.org/trac/spip-zone/changeset/104154

  • ffmpeg : specify/force pixel format for input H.264 video

    30 juillet 2017, par AndreG

    I have some MP4 video files missing the pixel format in their header information. I have already tried setting probesize and analyzeduration to their maximum values 2147483647 but that didn’t help.

    So I know these videos are probably corrupt but if this is the only information missing I was thinking I could maybe recover them by rebuilding their header information or somehow decoding them by forcing a pixel format. Does anyone have any idea if this is possible ? Some more background on the file :

    Mediainfo :

    $ mediainfo DJI_0090.MOV 
    
General
    
Complete name                            : DJI_0090.MOV
    
Format                                   : MPEG-4
    
Format profile                           : QuickTime
    
Codec ID                                 : qt   2014.02 (qt  )
    
File size                                : 165 MiB
    
Duration                                 : 22 s 322 ms
    
Overall bit rate mode                    : Variable
    
Overall bit rate                         : 61.8 Mb/s
    
Encoded date                             : UTC 2017-05-31 18:04:45
    
Tagged date                              : UTC 2017-05-31 18:04:45
    
Comment                                  : 0.9.145
    
©gpt                                     : -170.60
    
©gyw                                     : +157.30
    
©grl                                     : +0.00
    
IsTruncated                              : Yes
    

    
Video
    
ID                                       : 1
    
Format                                   : AVC
    
Format/Info                              : Advanced Video Codec
    
Format profile                           : High@L4.2
    
Format settings, CABAC                   : Yes
    
Format settings, RefFrames               : 1 frame
    
Codec ID                                 : avc1
    
Codec ID/Info                            : Advanced Video Coding
    
Duration                                 : 22 s 322 ms
    
Bit rate mode                            : Variable
    
Bit rate                                 : 59.4 Mb/s
    
Maximum bit rate                         : 50.0 Mb/s
    
Width                                    : 1 920 pixels
    
Height                                   : 1 080 pixels
    
Display aspect ratio                     : 16:9
    
Frame rate mode                          : Constant
    
Frame rate                               : 59.940 (60000/1001) FPS
    
Color space                              : YUV
    
Chroma subsampling                       : 4:2:0
    
Bit depth                                : 8 bits
    
Scan type                                : Progressive
    
Bits/(Pixel*Frame)                       : 0.478
    
Stream size                              : 158 MiB (96%)
    
Title                                    : DJI.AVC
    
Language                                 : English
    
Encoded date                             : UTC 2017-05-31 18:04:45
    
Tagged date                              : UTC 2017-05-31 18:04:45
    
Color range                              : Limited
    
Color primaries                          : BT.709
    
Transfer characteristics                 : BT.709
    
Matrix coefficients                      : BT.709

    ffprobe :

    $ ffprobe -analyzeduration 2147483647 -probesize 2147483647 DJI_0090.MOV 
    
ffprobe version 3.3.2 Copyright (c) 2007-2017 the FFmpeg developers
    
  built with Apple LLVM version 8.1.0 (clang-802.0.42)
    
  configuration: --prefix=/usr/local/Cellar/ffmpeg/3.3.2 --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-hardcoded-tables     --enable-avresample --cc=clang --host-cflags= --host-ldflags= --disable-indev=qtkit --enable-ffplay --enable-libfdk-aac --enable-libmp3lame     --enable-libsoxr --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-libzimg --enable-opencl --disable-lzma     --enable-libopenjpeg --disable-decoder=jpeg2000 --extra-cflags=-I/usr/local/Cellar/openjpeg/2.1.2_1/include/openjpeg-2.1 --enable-nonfree     --enable-vda
    
  libavutil      55. 58.100 / 55. 58.100
    
  libavcodec     57. 89.100 / 57. 89.100
    
  libavformat    57. 71.100 / 57. 71.100
    
  libavdevice    57.  6.100 / 57.  6.100
    
  libavfilter     6. 82.100 /  6. 82.100
    
  libavresample   3.  5.  0 /  3.  5.  0
    
  libswscale      4.  6.100 /  4.  6.100
    
  libswresample   2.  7.100 /  2.  7.100
    
  libpostproc    54.  5.100 / 54.  5.100
    
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7fc2e9002600] Could not find codec parameters for stream 0 (Video: h264 (avc1 / 0x31637661), none, 1920x1080):     unspecified pixel format
    
Consider increasing the value for the 'analyzeduration' and 'probesize' options
    
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'DJI_0090.MOV':
    
  Metadata:
    
    major_brand     : qt  
    
    minor_version   : 538182144
    
    compatible_brands: qt  
    
    creation_time   : 2017-05-31T18:04:45.000000Z
    
    comment         : 0.9.145
    
  Duration: 00:00:22.36, bitrate: 61732 kb/s
    
    Stream #0:0(eng): Video: h264 (avc1 / 0x31637661), none, 1920x1080, 59.94 fps, 59.94 tbr, 60k tbn, 120k tbc (default)
    
    Metadata:
    
      creation_time   : 2017-05-31T18:04:45.000000Z
    
      handler_name    : DJI.AVC
    
      encoder         : Dji AVC encoder

    I can’t force the pixel_format on ffmpeg this way :

    $ ffmpeg -pixel_format yuv420p -i DJI_0090.MOV test.mp4
    
ffmpeg version 3.3.2 Copyright (c) 2000-2017 the FFmpeg developers
    
  built with Apple LLVM version 8.1.0 (clang-802.0.42)
    
  configuration: --prefix=/usr/local/Cellar/ffmpeg/3.3.2 --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-hardcoded-tables     --enable-avresample --cc=clang --host-cflags= --host-ldflags= --disable-indev=qtkit --enable-ffplay --enable-libfdk-aac --enable-libmp3lame     --enable-libsoxr --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-libzimg --enable-opencl --disable-lzma     --enable-libopenjpeg --disable-decoder=jpeg2000 --extra-cflags=-I/usr/local/Cellar/openjpeg/2.1.2_1/include/openjpeg-2.1 --enable-nonfree     --enable-vda
    
  libavutil      55. 58.100 / 55. 58.100
    
  libavcodec     57. 89.100 / 57. 89.100
    
  libavformat    57. 71.100 / 57. 71.100
    
  libavdevice    57.  6.100 / 57.  6.100
    
  libavfilter     6. 82.100 /  6. 82.100
    
  libavresample   3.  5.  0 /  3.  5.  0
    
  libswscale      4.  6.100 /  4.  6.100
    
  libswresample   2.  7.100 /  2.  7.100
    
  libpostproc    54.  5.100 / 54.  5.100
    
Option pixel_format not found.

    Is there any other way to accomplish this with ffmpeg ? Is it possible to edit their header information to include the pixel format information ?

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