Why does padding (after crop/scale) seem to compress this video
horizontally?
Input #0, mpeg, from 'TEMP-original.vob':
Duration: 01:24:52.03, start: 0.287267, bitrate: 5841 kb/s
Stream #0:0[0x1e0]: Video: mpeg2video (Main), yuv420p(tv, top first),
720x576 [SAR 16:15 DAR 4:3], 25 fps, 25 tbr, 90k tbn, 50 tbc
Stream #0:1[0x80]: Audio: ac3, 48000 Hz, stereo, fltp, 224 kb/s
The actual video part (not including black bars) is (704:416:2:82)
according to cropdetect.
I'd like to end up with a video that's cropped to 704:416:2:82, scaled to
720x-1, padded to 720x480 with black bars only on the top/bottom, and a
DAR of 16:9 instead of 4:3. Not necessarily in that order... I'm not sure
of the "correct" filter order.
If all I do is crop the video to 704:416:2:82 it looks fine compared to
the original (complete output below):
$ ffmpeg -i TEMP-original.vob -codec:v mpeg2video -b:v 16384k -bufsize 4096k
-maxrate 30000k -codec:a copy -vf crop=704:416:2:82 -t 60 -f vob TEMP-crop.mpg
If I crop and scale to 720x-1 it still looks fine (complete output below):
$ ffmpeg -i TEMP-original.vob -codec:v mpeg2video -b:v 16384k -bufsize 4096k
-maxrate 30000k -codec:a copy -vf crop=704:416:2:82,scale=720:-1 -t 60 -f vob
TEMP-crop-scale.mpg
BUT, if I try to crop, scale and pad the top/bottom to 720x480, then the
video is compressed horizontally (complete output below):
$ ffmpeg -i TEMP-original.vob -codec:v mpeg2video -b:v 16384k -bufsize 4096k
-maxrate 30000k -codec:a copy -vf
crop=704:416:2:82,scale=720:-1,pad=720:480:0:27 -t 60 -f vob
TEMP-crop-scale.pad.mpg
FYI. The crop/scale ends up as 720x425, so to get to 720x480 I pad top
with 27 (480-425/2 = 27.5).
Why does padding cause the video to be compressed horizontally and more
importantly, how can I convert the original to 720x480 with bars only on
the top/bottom, DAR of 16/9, WITHOUT distorting the video?
-------------------------------------------------------------------------------
Complete output for all 3 example commands
-------------------------------------------------------------------------------
Crop to "cropdetect" size (704:416:2:82)
This looks fine (via ffplay) compared to original - it is not distorted
$ ffmpeg -i TEMP-original.vob -codec:v mpeg2video -b:v 16384k -bufsize 4096k
-maxrate 30000k -codec:a copy -vf crop=704:416:2:82 -t 60 -f vob TEMP-crop.mpg
ffmpeg version N-96491-g4b4bcb126c Copyright (c) 2000-2020 the FFmpeg
developers
built with gcc 9 (GCC)
configuration: --enable-gpl --enable-version3 --enable-nonfree
--enable-static --disable-shared --disable-debug --enable-libass
--enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus
--enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264
--enable-libx265 --enable-openssl --enable-libbluray --enable-libcdio
libavutil 56. 38.100 / 56. 38.100
libavcodec 58. 66.101 / 58. 66.101
libavformat 58. 35.104 / 58. 35.104
libavdevice 58. 9.103 / 58. 9.103
libavfilter 7. 71.100 / 7. 71.100
libswscale 5. 6.100 / 5. 6.100
libswresample 3. 6.100 / 3. 6.100
libpostproc 55. 6.100 / 55. 6.100
Input #0, mpeg, from 'TEMP-original.vob':
Duration: 01:24:52.03, start: 0.287267, bitrate: 5841 kb/s
Stream #0:0[0x1e0]: Video: mpeg2video (Main), yuv420p(tv, top first),
720x576 [SAR 16:15 DAR 4:3], 25 fps, 25 tbr, 90k tbn, 50 tbc
Stream #0:1[0x80]: Audio: ac3, 48000 Hz, stereo, fltp, 224 kb/s
Stream mapping:
Stream #0:0 -> #0:0 (mpeg2video (native) -> mpeg2video (native))
Stream #0:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
Output #0, vob, to 'TEMP-crop.mpg':
Metadata:
encoder : Lavf58.35.104
Stream #0:0: Video: mpeg2video (Main), yuv420p, 704x416 [SAR 16:15 DAR
352:195], q=2-31, 16384 kb/s, 25 fps, 90k tbn, 25 tbc
Metadata:
encoder : Lavc58.66.101 mpeg2video
Side data:
cpb: bitrate max/min/avg: 30000000/0/16384000 buffer size: 4096000
vbv_delay: N/A
Stream #0:1: Audio: ac3, 48000 Hz, stereo, fltp, 224 kb/s
[mpeg @ 0x21833c0] New subtitle stream 0:2 at pos:6678542 and
DTS:20.2873sbits/s speed=20.8x
[mpeg @ 0x21833c0] New subtitle stream 0:3 at pos:7571470 and DTS:22.5673s
frame= 1500 fps=489 q=2.0 Lsize= 34656kB time=00:00:59.96
bitrate=4734.2kbits/s speed=19.6x
video:32580kB audio:1641kB subtitle:0kB other streams:0kB global headers:0kB
muxing overhead: 1.272054%
$ ffmpeg -hide_banner -i TEMP-crop.mpg
Input #0, mpeg, from 'TEMP-crop.mpg':
Duration: 00:01:00.00, start: 0.540000, bitrate: 4731 kb/s
Stream #0:0[0x1e0]: Video: mpeg2video (Main), yuv420p(tv, progressive),
704x416 [SAR 104:99 DAR 16:9], 25 fps, 25 tbr, 90k tbn, 50 tbc
Stream #0:1[0x80]: Audio: ac3, 48000 Hz, stereo, fltp, 224 kb/s
At least one output file must be specified
Crop to "cropdetect" size (704:416:2:82) and scale to 720x-1 (ends up as
720x425)
This still looks fine (via ffplay) compared to original - it is not distorted
$ ffmpeg -i TEMP-original.vob -codec:v mpeg2video -b:v 16384k -bufsize 4096k
-maxrate 30000k -codec:a copy -vf crop=704:416:2:82,scale=720:-1 -t 60 -f vob
TEMP-crop-scale.mpg
ffmpeg version N-96491-g4b4bcb126c Copyright (c) 2000-2020 the FFmpeg
developers
built with gcc 9 (GCC)
configuration: --enable-gpl --enable-version3 --enable-nonfree
--enable-static --disable-shared --disable-debug --enable-libass
--enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus
--enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264
--enable-libx265 --enable-openssl --enable-libbluray --enable-libcdio
libavutil 56. 38.100 / 56. 38.100
libavcodec 58. 66.101 / 58. 66.101
libavformat 58. 35.104 / 58. 35.104
libavdevice 58. 9.103 / 58. 9.103
libavfilter 7. 71.100 / 7. 71.100
libswscale 5. 6.100 / 5. 6.100
libswresample 3. 6.100 / 3. 6.100
libpostproc 55. 6.100 / 55. 6.100
Input #0, mpeg, from 'TEMP-original.vob':
Duration: 01:24:52.03, start: 0.287267, bitrate: 5841 kb/s
Stream #0:0[0x1e0]: Video: mpeg2video (Main), yuv420p(tv, top first),
720x576 [SAR 16:15 DAR 4:3], 25 fps, 25 tbr, 90k tbn, 50 tbc
Stream #0:1[0x80]: Audio: ac3, 48000 Hz, stereo, fltp, 224 kb/s
Stream mapping:
Stream #0:0 -> #0:0 (mpeg2video (native) -> mpeg2video (native))
Stream #0:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
[swscaler @ 0x3ad3bc0] Warning: data is not aligned! This can lead to a speed
loss
Output #0, vob, to 'TEMP-crop-scale.mpg':
Metadata:
encoder : Lavf58.35.104
Stream #0:0: Video: mpeg2video (Main), yuv420p, 720x425 [SAR 374:351 DAR
352:195], q=2-31, 16384 kb/s, 25 fps, 90k tbn, 25 tbc
Metadata:
encoder : Lavc58.66.101 mpeg2video
Side data:
cpb: bitrate max/min/avg: 30000000/0/16384000 buffer size: 4096000
vbv_delay: N/A
Stream #0:1: Audio: ac3, 48000 Hz, stereo, fltp, 224 kb/s
[mpeg @ 0x397b3c0] New subtitle stream 0:2 at pos:6678542 and
DTS:20.2873sbits/s speed=16.3x
[mpeg @ 0x397b3c0] New subtitle stream 0:3 at pos:7571470 and DTS:22.5673s
frame= 1500 fps=376 q=2.0 Lsize= 32602kB time=00:00:59.96
bitrate=4453.6kbits/s speed= 15x
video:30550kB audio:1641kB subtitle:0kB other streams:0kB global headers:0kB
muxing overhead: 1.278884%
$ ffmpeg -hide_banner -i TEMP-crop-scale.mpg
Input #0, mpeg, from 'TEMP-crop-scale.mpg':
Duration: 00:01:00.00, start: 0.540000, bitrate: 4451 kb/s
Stream #0:0[0x1e0]: Video: mpeg2video (Main), yuv420p(tv, progressive),
720x425 [SAR 85:81 DAR 16:9], 25 fps, 25 tbr, 90k tbn, 50 tbc
Stream #0:1[0x80]: Audio: ac3, 48000 Hz, stereo, fltp, 224 kb/s
At least one output file must be specified
Crop to "cropdetect" size (704:416:2:82), scale to 720x-1 and pad top/bottom to
720x480
This is compressed horizontally (via ffplay) compared to original
$ ffmpeg -i TEMP-original.vob -codec:v mpeg2video -b:v 16384k -bufsize 4096k
-maxrate 30000k -codec:a copy -vf
crop=704:416:2:82,scale=720:-1,pad=720:480:0:27 -t 60 -f vob
TEMP-crop-scale-pad.mpg
ffmpeg version N-96491-g4b4bcb126c Copyright (c) 2000-2020 the FFmpeg
developers
built with gcc 9 (GCC)
configuration: --prefix=/usr/local/ffmpeg-master-20200125 --enable-gpl
--enable-version3 --enable-nonfree --enable-static --disable-shared
--disable-debug --enable-libass --enable-libfdk-aac --enable-libfreetype
--enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis
--enable-libvpx --enable-libx264 --enable-libx265 --enable-openssl
--enable-libbluray --enable-libcdio
libavutil 56. 38.100 / 56. 38.100
libavcodec 58. 66.101 / 58. 66.101
libavformat 58. 35.104 / 58. 35.104
libavdevice 58. 9.103 / 58. 9.103
libavfilter 7. 71.100 / 7. 71.100
libswscale 5. 6.100 / 5. 6.100
libswresample 3. 6.100 / 3. 6.100
libpostproc 55. 6.100 / 55. 6.100
Input #0, mpeg, from 'TEMP-original.vob':
Duration: 01:24:52.03, start: 0.287267, bitrate: 5841 kb/s
Stream #0:0[0x1e0]: Video: mpeg2video (Main), yuv420p(tv, top first),
720x576 [SAR 16:15 DAR 4:3], 25 fps, 25 tbr, 90k tbn, 50 tbc
Stream #0:1[0x80]: Audio: ac3, 48000 Hz, stereo, fltp, 224 kb/s
Stream mapping:
Stream #0:0 -> #0:0 (mpeg2video (native) -> mpeg2video (native))
Stream #0:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
[swscaler @ 0x254fbc0] Warning: data is not aligned! This can lead to a speed
loss
Output #0, vob, to 'TEMP-crop-scale-pad.mpg':
Metadata:
encoder : Lavf58.35.104
Stream #0:0: Video: mpeg2video (Main), yuv420p, 720x480 [SAR 374:351 DAR
187:117], q=2-31, 16384 kb/s, 25 fps, 90k tbn, 25 tbc
Metadata:
encoder : Lavc58.66.101 mpeg2video
Side data:
cpb: bitrate max/min/avg: 30000000/0/16384000 buffer size: 4096000
vbv_delay: N/A
Stream #0:1: Audio: ac3, 48000 Hz, stereo, fltp, 224 kb/s
[mpeg @ 0x23f73c0] New subtitle stream 0:2 at pos:6678542 and
DTS:20.2873sbits/s speed=16.3x
[mpeg @ 0x23f73c0] New subtitle stream 0:3 at pos:7571470 and DTS:22.5673s
frame= 1500 fps=369 q=2.0 Lsize= 32856kB time=00:00:59.96
bitrate=4488.3kbits/s speed=14.7x
video:30800kB audio:1641kB subtitle:0kB other streams:0kB global headers:0kB
muxing overhead: 1.280809%
$ ffmpeg -hide_banner -i TEMP-crop-scale-pad.mpg
Input #0, mpeg, from 'TEMP-crop-scale-pad.mpg':
Duration: 00:01:00.00, start: 0.540000, bitrate: 4485 kb/s
Stream #0:0[0x1e0]: Video: mpeg2video (Main), yuv420p(tv, progressive),
720x480 [SAR 1:1 DAR 3:2], 25 fps, 25 tbr, 90k tbn, 50 tbc
Stream #0:1[0x80]: Audio: ac3, 48000 Hz, stereo, fltp, 224 kb/s
At least one output file must be specified
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