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• 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 ?

• ffmpeg with -strict -2 : Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height

  8 juin 2018, par Bhumi Shah

  This is my command

  ffmpeg -i a.mp4 -asyncec libx264 -strict -2 -refs 6 -coder 1 -sc_threshold 40 -flags +loop -me_range 16 -subq 7 -i_qfactor 0.71 -qcomp 0.6 -qdiff 4 -trellis 1 -b:a 128k -pass 1 -profile:v baseline -level:v 3.0 -s 1080x1920 a.mp4

  Here is the error i am getting

  ffmpeg version N-46084-gcae004cab-static https://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2018 the FFmpeg developers
  
    built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
  
    configuration: --enable-gpl --enable-version3 --enable-static --disable-debug --disable-ffplay --disable-indev=sndio --disable-outdev=sndio --cc=gcc-6 --enable-fontconfig --enable-frei0r --enable-gnutls --enable-gray --enable-libaom --enable-libfribidi --enable-libass --enable-libvmaf --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librubberband --enable-libsoxr --enable-libspeex --enable-libvorbis --enable-libopus --enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzimg
  
    libavutil      56. 18.102 / 56. 18.102
  
    libavcodec     58. 19.101 / 58. 19.101
  
    libavformat    58. 13.102 / 58. 13.102
  
    libavdevice    58.  4.100 / 58.  4.100
  
    libavfilter     7. 22.100 /  7. 22.100
  
    libswscale      5.  2.100 /  5.  2.100
  
    libswresample   3.  2.100 /  3.  2.100
  
    libpostproc    55.  2.100 / 55.  2.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'a.mp4':
  
    Metadata:
  
      major_brand     : mp42
  
      minor_version   : 0
  
      compatible_brands: mp42mp41
  
      creation_time   : 2018-01-17T06:39:29.000000Z
  
    Duration: 00:00:06.04, start: 0.000000, bitrate: 872 kb/s
  
      Stream #0:0(eng): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt709), 2160x3840, 534 kb/s, 30 fps, 30 tbr, 30k tbn, 60 tbc (default)
  
      Metadata:
  
        creation_time   : 2018-01-17T06:39:29.000000Z
  
        handler_name    : Alias Data Handler
  
        encoder         : AVC Coding
  
      Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 317 kb/s (default)
  
      Metadata:
  
        creation_time   : 2018-01-17T06:39:29.000000Z
  
        handler_name    : Alias Data Handler
  
  File 'a.mp4' already exists. Overwrite ? [y/N] y
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
  
    Stream #0:1 -> #0:1 (aac (native) -> aac (native))
  
  Press [q] to stop, [?] for help
  
  [libx264 @ 0x66327c0] frame MB size (68x120) > level limit (1620)
  
  [libx264 @ 0x66327c0] DPB size (1 frames, 8160 mbs) > level limit (0 frames, 8100 mbs)
  
  [libx264 @ 0x66327c0] MB rate (244800) > level limit (40500)
  
  [libx264 @ 0x66327c0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
  
  [libx264 @ 0x66327c0] ratecontrol_init: can't open stats file
  
  Error initializing output stream 0:0 -- Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height
  
  Conversion failed!

• ffmpeg h.246 plays locally in Safari, but not when hosted on s3 bucket

  7 juin 2018, par Simon Rogers

  ffmpeg h.246 plays locally in Safari, but not when hosted on s3 bucket.

  I thought it was therefore a problem with S3, however a friend has sent me an .mp4 of the same file converted with Zencoder’s service and this works perfectly, which surely means it must be a problem with my encoding settings in ffmpeg ?

  I’m using the settings recommended for maximum compatibility :

  ffmpeg -an -i mov-input-02.mov -vcodec libx264 -filter:v scale="1400:trunc(ow/a/2)*2" -movflags +faststart -pix_fmt yuv420p -profile:v baseline mov-output-02-1400.mp4

  Additionally, the .webm files I’m converting with ffmpeg all work perfectly in Chrome, Firefox, Opera etc.!

  I would really appreciate any thoughts.

  The video that works from Zencoder has this metadata :

  major_brand     : isom
  
  minor_version   : 1
  
  compatible_brands: isomavc1mp42
  
  creation_time   : 2018-06-01T11:24:54.000000Z
  
  Duration: 00:00:10.97, start: 0.000000, bitrate: 396 kb/s
  
  Stream #0:0(und): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p(tv, bt709), 1800x1200 [SAR 1:1 DAR 3:2], 394 kb/s, 30 fps, 30 tbr, 30 tbn, 60 tbc (default)
  
  Metadata:
  
    creation_time   : 2018-06-01T11:24:49.000000Z

  While my videos from ffmpeg which don’t work have this metadata :

  Metadata:
  
  major_brand     : isom
  
  minor_version   : 512
  
  compatible_brands: isomiso2avc1mp41
  
  encoder         : Lavf58.12.100
  
  Duration: 00:00:10.97, start: 0.000000, bitrate: 184 kb/s
  
  Stream #0:0(eng): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p, 1400x932 [SAR 699:700 DAR 3:2], 182 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
  
  Metadata:
  
    handler_name    : VideoHandler
  
    timecode        : 00:00:00:01
  
  Stream #0:1(eng): Data: none (tmcd / 0x64636D74), 0 kb/s
  
  Metadata:
  
    handler_name    : TimeCodeHandler
  
    timecode        : 00:00:00:01
  
  Unsupported codec with id 0 for input stream 1

  Here’s the full output from conversion :

      Tempuras-iMac:2018.06.05 tempura$ ffmpeg -an -i mov-input-01.mov -vcodec l      Tempuras-iMac:2018.06.05 tempura$ ffmpeg -an -i mov-input-02.mov -vcodec libx264 -filter:v scale="1400:trunc(ow/a/2)*2" -movflags +faststart -pix_fmt yuv420p -profile:v baseline -level 3 mov-output-02-1400.mp4 
  
      ffmpeg version 4.0 Copyright (c) 2000-2018 the FFmpeg developers
  
        built with Apple LLVM version 8.1.0 (clang-802.0.42)
  
        configuration: --prefix=/usr/local/Cellar/ffmpeg/4.0 --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-gpl --enable-libmp3lame --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxvid --enable-opencl --enable-videotoolbox --disable-lzma
  
        libavutil      56. 14.100 / 56. 14.100
  
        libavcodec     58. 18.100 / 58. 18.100
  
        libavformat    58. 12.100 / 58. 12.100
  
        libavdevice    58.  3.100 / 58.  3.100
  
        libavfilter     7. 16.100 /  7. 16.100
  
        libavresample   4.  0.  0 /  4.  0.  0
  
        libswscale      5.  1.100 /  5.  1.100
  
        libswresample   3.  1.100 /  3.  1.100
  
        libpostproc    55.  1.100 / 55.  1.100
  
      Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'mov-input-02.mov':
  
        Metadata:
  
          major_brand     : qt  
  
          minor_version   : 537199360
  
          compatible_brands: qt  
  
          creation_time   : 2018-05-09T09:59:58.000000Z
  
        Duration: 00:00:10.97, start: 0.000000, bitrate: 114375 kb/s
  
          Stream #0:0(eng): Video: qtrle (rle  / 0x20656C72), rgb24(progressive), 2700x1800, 113610 kb/s, SAR 1:1 DAR 3:2, 30 fps, 30 tbr, 30 tbn, 30 tbc (default)
  
          Metadata:
  
            creation_time   : 2018-05-09T09:59:58.000000Z
  
            handler_name    : Apple Alias Data Handler
  
            encoder         : Animation
  
            timecode        : 00:00:00:01
  
          Stream #0:1(eng): Data: none (tmcd / 0x64636D74), 0 kb/s (default)
  
          Metadata:
  
            creation_time   : 2018-05-09T09:59:58.000000Z
  
            handler_name    : Apple Alias Data Handler
  
            timecode        : 00:00:00:01
  
      Stream mapping:
  
        Stream #0:0 -> #0:0 (qtrle (native) -> h264 (libx264))
  
      Press [q] to stop, [?] for help
  
      [libx264 @ 0x7fac39004200] using SAR=699/700
  
      [libx264 @ 0x7fac39004200] frame MB size (88x59) > level limit (1620)
  
      [libx264 @ 0x7fac39004200] MB rate (155760) > level limit (40500)
  
      [libx264 @ 0x7fac39004200] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
  
      [libx264 @ 0x7fac39004200] profile Constrained Baseline, level 3.0
  
      [libx264 @ 0x7fac39004200] 264 - core 152 r2854 e9a5903 - H.264/MPEG-4 AVC codec - Copyleft 2003-2017 - http://www.videolan.org/x264.html - options: cabac=0 ref=1 deblock=1:0:0 analyse=0x1:0x111 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=1 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=6 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=0 weightp=0 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
  
      Output #0, mp4, to 'mov-output-02-1400.mp4':
  
        Metadata:
  
          major_brand     : qt  
  
          minor_version   : 537199360
  
          compatible_brands: qt  
  
          encoder         : Lavf58.12.100
  
          Stream #0:0(eng): Video: h264 (libx264) (avc1 / 0x31637661), yuv420p, 1400x932 [SAR 699:700 DAR 3:2], q=-1--1, 0.03 fps, 15360 tbn, 30 tbc (default)
  
          Metadata:
  
            creation_time   : 2018-05-09T09:59:58.000000Z
  
            handler_name    : Apple Alias Data Handler
  
            timecode        : 00:00:00:01
  
            encoder         : Lavc58.18.100 libx264
  
          Side data:
  
            cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
  
      [mp4 @ 0x7fac39003000] Starting second pass: moving the moov atom to the beginning of the file     
  
      frame=  329 fps= 42 q=-1.0 Lsize=     248kB time=00:00:10.93 bitrate= 185.5kbits/s speed= 1.4x    
  
      video:245kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.042892%
  
      [libx264 @ 0x7fac39004200] frame I:2     Avg QP:15.82  size: 34370
  
      [libx264 @ 0x7fac39004200] frame P:327   Avg QP:16.88  size:   555
  
      [libx264 @ 0x7fac39004200] mb I  I16..4: 76.8%  0.0% 23.2%
  
      [libx264 @ 0x7fac39004200] mb P  I16..4:  0.5%  0.0%  0.2%  P16..4:  0.7%  0.2%  0.1%  0.0%  0.0%    skip:98.3%
  
      [libx264 @ 0x7fac39004200] coded y,uvDC,uvAC intra: 14.3% 0.1% 0.1% inter: 0.2% 0.0% 0.0%
  
      [libx264 @ 0x7fac39004200] i16 v,h,dc,p: 57% 39%  3%  0%
  
      [libx264 @ 0x7fac39004200] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 41% 24% 20%  2%  3%  3%  2%  3%  1%
  
      [libx264 @ 0x7fac39004200] i8c dc,h,v,p: 100%  0%  0%  0%
  
      [libx264 @ 0x7fac39004200] kb/s:182.53