I have a 30-fps video just downloaded by youtube-dl
, and it seems to have black frames in the beginning of it.
Part of the result of ffprobe youtube-dl.mp4
:
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'youtube-dl.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.43.100
Duration: 00:04:53.69, start: 0.000000, bitrate: 1250 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1280x720 [SAR 1:1 DAR 16:9], 1115 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
Metadata:
handler_name : ISO Media file produced by Google Inc.
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 127 kb/s (default)
Metadata:
handler_name : ISO Media file produced by Google Inc.
Then I tried to trim the video using ffmpeg -i youtube-dl.mp4 -ss 0:0:0 -to 0:4:37 -vcodec copy -acodec copy youtube-dl-trimmed.mp4
. Part of the result is below:
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'youtube-dl.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.43.100
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1280x720 [SAR 1:1 DAR 16:9], 1115 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
Metadata:
handler_name : ISO Media file produced by Google Inc.
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 127 kb/s (default)
Metadata:
handler_name : ISO Media file produced by Google Inc.
Output #0, mp4, to 'youtube-dl-trimmed.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.43.100
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1280x720 [SAR 1:1 DAR 16:9], q=2-31, 1115 kb/s, 30 fps, 30 tbr, 15360 tbn, 15360 tbc (default)
Metadata:
handler_name : ISO Media file produced by Google Inc.
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 127 kb/s (default)
Metadata:
handler_name : ISO Media file produced by Google Inc.
Stream mapping:
Stream #0:0 -> #0:0 (copy)
Stream #0:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
frame= 8288 fps=0.0 q=-1.0 Lsize= 43944kB time=00:04:36.99 bitrate=1299.6kbits/s speed= 382x
video:39364kB audio:4329kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.575328%
And use ffprobe
to probe it:
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'youtube-dl-trimmed.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.43.100
Duration: 00:04:37.02, start: 0.000000, bitrate: 1299 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1280x720 [SAR 1:1 DAR 16:9], 1167 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
Metadata:
handler_name : ISO Media file produced by Google Inc.
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
Metadata:
handler_name : ISO Media file produced by Google Inc.
What I wonder is that the playback results of some applications and video processing libraries vary. In some of them the video still remains the black frames, but in the others the first 22 frames disappear and certainly the total number of frames is decreased. The test result about the black frames is below:
Applications or Libraries | youtube-dl.mp4 | youtube-dl-trimmed.mp4 |
---|---|---|
ffplay | remained | disappeared |
PotPlayer | remained | remained |
VLC Player | remained | remained |
Aegisub | remained | disappeared |
Adobe Premiere | remained | remained |
OpenCV library | remained | disappeared |
It bothers me a lot because I use Aegisub to create ASS subtitles but I use FFmpeg to burn a subtitle into youtube-dl-trimmed.mp4
, the black frames remain and thus the showing time of every line isn't fit with the speakers' words. Also the black frames still here when using ffplay
to play the hard-subtitled video. What's wrong with these videos? Does youtube-dl-trimmed.mp4
have dropped frames? Any reply is appreciated.
EDIT:
Version string and configuration options of my ffmpeg
:
ffmpeg version git-2020-05-15-b18fd2b Copyright (c) 2000-2020 the FFmpeg developers
built with gcc 9.3.1 (GCC) 20200513
configuration: --enable-gpl --enable-version3 --enable-sdl2
--enable-fontconfig --enable-gnutls --enable-iconv --enable-libass
--enable-libdav1d --enable-libbluray --enable-libfreetype
--enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb
--enable-libopenjpeg --enable-libopus --enable-libshine
--enable-libsnappy --enable-libsoxr --enable-libsrt --enable-libtheora
--enable-libtwolame --enable-libvpx --enable-libwavpack
--enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2
--enable-libzimg --enable-lzma --enable-zlib --enable-gmp
--enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvo-amrwbenc
--enable-libmysofa --enable-libspeex --enable-libxvid
--enable-libaom --disable-w32threads --enable-libmfx --enable-ffnvcodec
--enable-cuda-llvm --enable-cuvid --enable-d3d11va
--enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth
--enable-libopenmpt --enable-amf
libavutil 56. 45.100 / 56. 45.100
libavcodec 58. 84.100 / 58. 84.100
libavformat 58. 43.100 / 58. 43.100
libavdevice 58. 9.103 / 58. 9.103
libavfilter 7. 81.100 / 7. 81.100
libswscale 5. 6.101 / 5. 6.101
libswresample 3. 6.100 / 3. 6.100
libpostproc 55. 6.100 / 55. 6.100
EDIT 2:
@slhck provided a workaround in the comments. Re-encoding the video can keep all players behaving well.
-ss 0:0:0 -to 0:4:37
to trim off frames in the beginning? You start at 0; there is nothing before 0. If you wanted to trim off some frames,ss
should be a positive number. Please always show the complete uncut command line output.-ss 0:0:0
because I didn't want to calculate how long the black frames lasted and they just lasted less than a second in fact, then I decided to keep the frames. And the command line output is full actually. As for the uncut output, I have just added the configuration options and version string to the post. These things and the part of the result makes up the full output.-ss 0
), the players show different behavior? What if you re-encode with-c:v libx264 -crf 18
instead of-vcodec copy
, what happens?-ss
so that the black frames disappear. I am quite sure there's no easy way around this, in particular if you want all players behaving the same.