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• frame appears 0.000057 second before pts_time using ffmpeg

  17 septembre 2020, par Lincolnhuj

  This video is created using ffmpeg command from a series of images with number and expected timestamp on it (assuming 120 fps constant frame rate) :

  


  ffmpeg -framerate 120 -i %03d.png -crf 0 -x264opts keyint=1:min-keyint=1 120.mp4


  


  It's supposed to be constant frame rate, and all the frames are I frames.
I expect frame 6 will show up exactly at time 0.05 second [0.05, 0.0583333), as the pts_time shown in ffmpeg and ffprobe :

  


  


  [Parsed_showinfo_0 @ 0x7fba11404080] n : 6 pts : 768 pts_time:0.05
pos : 36021 fmt:yuv444p sar:0/1 s:1552x878 i:P iskey:1 type:I
checksum:2CDED07A plane_checksum :[A86DBAAD C4CB8EF2 DDC586CC]
mean :[163 133 121 ] stdev :[9.0 0.6 0.8 ]

  


  [FRAME]
media_type=video
stream_index=0
key_frame=1
pkt_pts=768
pkt_pts_time=0.050000
pkt_dts=768
pkt_dts_time=0.050000
best_effort_timestamp=768
best_effort_timestamp_time=0.050000
pkt_duration=128
pkt_duration_time=0.008333
pkt_pos=36021
pkt_size=2531
width=1552
height=878
pix_fmt=yuv444p
sample_aspect_ratio=N/A
pict_type=I
coded_picture_number=6
display_picture_number=0
interlaced_frame=0
top_field_first=0
repeat_pict=0
color_range=unknown
color_space=unknown
color_primaries=unknown
color_transfer=unknown
chroma_location=left
[/FRAME]


  


  


  But in reality, it shows up since 0.049943 second. I use ffmpeg to extract that time with 0.0001 second duration

  


  ffmpeg -ss 00:00:00.049943 -i 120_keyint_1.mp4 -t 00:00:00.0001 out.mp4


  


  and get this video, which shows frame 6.

  


  I also tried playing this video on chrome, and set the currentTime of videoNode. It shows frame 5 at 0.049943, but shows frame 6 since 0.049968 (before 0.05 !).

  


  However, I tried another encoding method and get another constant frame rate video :

  


  ffmpeg -framerate 120 -i %03d.png -vcodec libx264 -f mp4 -movflags faststart 120.mp4


  


  theoretically frame 6 should also appear in time range [0.05, 0.0583333), but in Chrome frame 6 will not show up until currentTime >= 0.051 second. More interestingly, I get frame 6 at 0.049943 second using ffmpeg, the same extraction command above.

  


  Does this mean in MPEG4 h.264 video, we cannot rely on pts_time from ffmpeg to determine exact show time of a specific frame and it's video player specific ?

  


• Splitting webm video to png with transparency

  31 août 2020, par Stephen Emslie

  I need to split a webm encoded video into png frames, without losing transparency. I use the following ffmpeg command :

  



  ffmpeg -i dancer1.webm -pix_fmt rgba frames/%04d.png


  



  This produces a directory of pngs, but why is each output frame is missing transparency ?

  



  I have used this example video, which contains an alpha channel. See it playing over a background here. Here's an example output frame from ffmpeg :

  



  

  



  ffmpeg produces the following output when it runs :

  



  ffmpeg version N-60294-g549f052 Copyright (c) 2000-2014 the FFmpeg developers                                             [1/2471]
  built on Feb  2 2014 05:41:56 with gcc 4.6 (Debian 4.6.3-1)
  configuration: --prefix=/root/ffmpeg-static/64bit --extra-cflags='-I/root/ffmpeg-static/64bit/include -static' --extra-ldflags='-L/root/ffmpeg-static/64bit/lib -static' --extra-libs='-lxml2 -lexpat -lfreetype' --enable-static --disable-shared --disable-ffserver --disable-doc --enable-bzlib --enable-zlib --enable-postproc --enable-runtime-cpudetect --enable-libx264 --enable-gpl --enable-libtheora --enable-libvorbis --enable-libmp3lame --enable-gray --enable-libass --enable-libfreetype --enable-libopenjpeg --enable-libspeex --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-version3 --enable-libvpx
  libavutil      52. 63.100 / 52. 63.100
  libavcodec     55. 49.101 / 55. 49.101
  libavformat    55. 28.101 / 55. 28.101
  libavdevice    55.  7.100 / 55.  7.100
  libavfilter     4.  1.101 /  4.  1.101
  libswscale      2.  5.101 /  2.  5.101
  libswresample   0. 17.104 /  0. 17.104
  libpostproc    52.  3.100 / 52.  3.100
Input #0, matroska,webm, from 'dancer1.webm':
  Metadata:
    encoder         : libwebm-0.2.1.0
  Duration: 00:01:02.83, start: 0.000000, bitrate: 520 kb/s
    Stream #0:0(eng): Video: vp8, yuv420p, 640x360, SAR 1:1 DAR 16:9, 30 tbr, 1k tbn, 1k tbc (default)
    Metadata:
      alpha_mode      : 1
Output #0, image2, to 'frames/%04d.png':
  Metadata:
    encoder         : Lavf55.28.101
    Stream #0:0(eng): Video: png, rgba, 640x360 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 90k tbn, 30 tbc (default)
Metadata:
  alpha_mode      : 1
Stream mapping:
  Stream #0:0 -> #0:0 (vp8 -> png)


  



  Running identify on an output png produces this :

  



  $ identify 0001.png
0001.png PNG 640x360 640x360+0+0 8-bit DirectClass 94.1KB 0.000u 0:00.000


  



  file has this to say about the png :

  



  $ file 0001.png
0001.png: PNG image data, 640 x 360, 8-bit/color RGBA, non-interlaced


  



  Everything looks about right to me, so why don't the output images contain an alpha channel ?

  


• ffmpeg segmentation fails with floating point exception

  19 août 2020, par painfulenglish

  I'm trying to segment a video using the following command :

  


  ffmpeg -i /home/user/videos/0001.MP4 -codec copy -map 0 -f segment -segment_frames 66 /tmp/boos/0001/0001_%03d.MP4


  


  After working for a few seconds, the output being

  


  frame=  251 fps=0.0 q=-1.0 size=N/A time=00:00:10.02 bitrate=N/A speed=19.6x    


  


  the process fails with a floating point exception. The full output is given below. I have a suspicion that the problem may be specific to GoPro videos due to the following observations :

  


  

  1. The same video is segmented successfully if I first re-encode it using ffmpeg.

  


  2. Other videos (non-GoPro) do not cause the problem.

  


  


  I would appreciate any suggestions on how to track down or even solve the problem.

  


  Full output :

  


  ffmpeg version 3.4.8-0ubuntu0.2 Copyright (c) 2000-2020 the FFmpeg developers&#xA;  built with gcc 7 (Ubuntu 7.5.0-3ubuntu1~18.04)&#xA;  configuration: --prefix=/usr --extra-version=0ubuntu0.2 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared&#xA;  libavutil      55. 78.100 / 55. 78.100&#xA;  libavcodec     57.107.100 / 57.107.100&#xA;  libavformat    57. 83.100 / 57. 83.100&#xA;  libavdevice    57. 10.100 / 57. 10.100&#xA;  libavfilter     6.107.100 /  6.107.100&#xA;  libavresample   3.  7.  0 /  3.  7.  0&#xA;  libswscale      4.  8.100 /  4.  8.100&#xA;  libswresample   2.  9.100 /  2.  9.100&#xA;  libpostproc    54.  7.100 / 54.  7.100&#xA;Input #0, mov,mp4,m4a,3gp,3g2,mj2, from &amp;apos;/home/broadbelt/videos/0001.MP4&amp;apos;:&#xA;  Metadata:&#xA;    major_brand     : mp41&#xA;    minor_version   : 538120216&#xA;    compatible_brands: mp41&#xA;    creation_time   : 2019-11-18T13:55:42.000000Z&#xA;    firmware        : HD7.01.01.80.00&#xA;  Duration: 00:17:38.22, start: 0.000000, bitrate: 30245 kb/s&#xA;    Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuvj420p(pc, bt709), 1920x1080 [SAR 1:1 DAR 16:9], 30000 kb/s, 25 fps, 25 tbr, 90k tbn, 50 tbc (default)&#xA;    Metadata:&#xA;      creation_time   : 2019-11-18T13:55:42.000000Z&#xA;      handler_name    : GoPro AVC  &#xA;      encoder         : GoPro AVC encoder&#xA;      timecode        : 13:55:42:21&#xA;    Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 189 kb/s (default)&#xA;    Metadata:&#xA;      creation_time   : 2019-11-18T13:55:42.000000Z&#xA;      handler_name    : GoPro AAC  &#xA;      timecode        : 13:55:42:21&#xA;    Stream #0:2(eng): Data: none (tmcd / 0x64636D74) (default)&#xA;    Metadata:&#xA;      creation_time   : 2019-11-18T13:55:42.000000Z&#xA;      handler_name    : GoPro TCD  &#xA;      timecode        : 13:55:42:21&#xA;    Stream #0:3(eng): Data: none (gpmd / 0x646D7067), 37 kb/s (default)&#xA;    Metadata:&#xA;      creation_time   : 2019-11-18T13:55:42.000000Z&#xA;      handler_name    : GoPro MET  &#xA;    Stream #0:4(eng): Data: none (fdsc / 0x63736466), 9 kb/s (default)&#xA;    Metadata:&#xA;      creation_time   : 2019-11-18T13:55:42.000000Z&#xA;      handler_name    : GoPro SOS  &#xA;<span style="background-color:#2E3436"><font color="#FF87FF">[segment @ 0x562a95062f40] </font></span>Opening &amp;apos;/tmp/boost/0001/0001_000.MP4&amp;apos; for writing&#xA;<span style="background-color:#2E3436"><font color="#FF87FF">[mp4 @ 0x562a9506a600] </font></span><span style="background-color:#2E3436"><font color="#FF0000">Timecode frame rate must be specified</font></span>&#xA;Output #0, segment, to &amp;apos;/tmp/boost/0001/0001_%03d.MP4&amp;apos;:&#xA;  Metadata:&#xA;    major_brand     : mp41&#xA;    minor_version   : 538120216&#xA;    compatible_brands: mp41&#xA;    firmware        : HD7.01.01.80.00&#xA;    encoder         : Lavf57.83.100&#xA;    Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuvj420p(pc, bt709), 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 30000 kb/s, 25 fps, 25 tbr, 12800 tbn, 25 tbc (default)&#xA;    Metadata:&#xA;      creation_time   : 2019-11-18T13:55:42.000000Z&#xA;      handler_name    : GoPro AVC  &#xA;      encoder         : GoPro AVC encoder&#xA;      timecode        : 13:55:42:21&#xA;    Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 189 kb/s (default)&#xA;    Metadata:&#xA;      creation_time   : 2019-11-18T13:55:42.000000Z&#xA;      handler_name    : GoPro AAC  &#xA;      timecode        : 13:55:42:21&#xA;    Stream #0:2(eng): Data: none (tmcd / 0x64636D74) (default)&#xA;    Metadata:&#xA;      creation_time   : 2019-11-18T13:55:42.000000Z&#xA;      handler_name    : GoPro TCD  &#xA;      timecode        : 13:55:42:21&#xA;    Stream #0:3(eng): Data: none (gpmd / 0x646D7067), 37 kb/s (default)&#xA;    Metadata:&#xA;      creation_time   : 2019-11-18T13:55:42.000000Z&#xA;      handler_name    : GoPro MET  &#xA;    Stream #0:4(eng): Data: none (fdsc / 0x63736466), 9 kb/s (default)&#xA;    Metadata:&#xA;      creation_time   : 2019-11-18T13:55:42.000000Z&#xA;      handler_name    : GoPro SOS  &#xA;Stream mapping:&#xA;  Stream #0:0 -&amp;gt; #0:0 (copy)&#xA;  Stream #0:1 -&amp;gt; #0:1 (copy)&#xA;  Stream #0:2 -&amp;gt; #0:2 (copy)&#xA;  Stream #0:3 -&amp;gt; #0:3 (copy)&#xA;  Stream #0:4 -&amp;gt; #0:4 (copy)&#xA;Press [q] to stop, [?] for help&#xA;**Floating point exception (core dumped)me=00:00:01.00 bitrate=N/A speed=0.143x**   &#xA;