[Cin] Possibly better conversion quality at 2x speed/ bitrate and 25fps/ 50 fps

Mon Feb 19 19:25:06 CET 2024

пн, 19 февр. 2024 г., 20:59 Terje J. Hanssen via Cin <
cin at lists.cinelerra-gg.org>:

> Thirty years ago I tape recordered some hundreds of old genealogy photos,
> which I now plan to convert from SD-DV files to burn on DVD video discs.
> The camcordings were made with fade in/out, zoom closeups and pan
> effects,  which fit well at 2x playback speed and with additional
> pause/play navigation on DVD videos.
>
> Signal/noise at 2x speed with same fps and bitrate (halph of the fps are
> dropped), should result in output with 1/2 playback duration and equivalent
> quality as normal speed.
>
> Yet I wonder if it possible in some way to achieve better quality if also
> 2x bitrate and fps are possible to utilize temporarily as a better quality
> base (downsampling), even if DVD video limits the fps and bitrate?
>

They are progressive (not interlaced) dv files, right? I only can think
about fields-> frames conversion, that changes both frame size and fps.
There might be some movement interpolation algorithms, or even neural nets
nowadays, but I can't see any use of it directly in ffmpeg (for one command
conversion) as long as output remain at 25 fps. But there might be some
sideefects that makes viewing better/worse?

Bitrate for consumer dv is fixed at 25Mbits, dv50 obviously goes above that
*2, but not sure if you  gain anything by transcoding into dv? (it was
important when other hardware worked with those files, or they were
transferred back to tape. But our current case is single Linux workstation
only..?). mpeg2 dvd video yeah, seems to have gard upper cap on how big
bitrate-wise it can go - you can try other stuff like custom matrixes and
see if they improve quality ...

I think there was yuvfps tool in mjpegtools, but I never used it ...

>
>
> Here are my test samples so far:
>
> du -sh dv95*
> 1)    2,0G    dv95.dv (input source)
>
> 2) 1,1G    dv95_2x_25fps.dv
> 3) 2,0G    dv95_2x_50fps.dv
>
> 4) 218M    dv95_2x_25fps.mpg
> 5) 218M    dv95_2x_50fps.mpg
>
>
> 1)
> ffprobe -hide_banner dv95.dv (source DV, Duration: 00:09:56.48)
>
> [dv @ 0x55d65d6ca080] Estimating duration from bitrate, this may be
> inaccurate
> Input #0, dv, from 'dv95.dv':
>   Metadata:
>     timecode        : 00:00:00:00
>   Duration: 00:09:56.48, start: 0.000000, bitrate: 28800 kb/s
>   Stream #0:0: Video: dvvideo, yuv420p, 720x576 [SAR 16:15 DAR 4:3], 28800
> kb/s, 60k fps, 25 tbr, 60k tbn
>   Stream #0:1: Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/s
>
>
>
> ffmpeg conversions using the FFmpeg setpts filter
>
> http://trac.ffmpeg.org/wiki/How%20to%20speed%20up%20/%20slow%20down%20a%20video#setptsfilter
>
>
> 2)
> ffmpeg -i dv95.dv -vf "setpts=0.5*PTS" -an dv95_2x_25fps.dv
>
> ffprobe -hide_banner dv95_2x_25fps.dv
>
> [dv @ 0x5582eb685080] Estimating duration from bitrate, this may be
> inaccurate
> Input #0, dv, from 'dv95_2x_25fps.dv':
>   Metadata:
>     timecode        : 00:00:00:00
>   Duration: 00:04:58.32, start: 0.000000, bitrate: 28800 kb/s
>   Stream #0:0: Video: dvvideo, yuv420p, 720x576 [SAR 16:15 DAR 4:3], 28800
> kb/s, 60k fps, 25 tbr, 60k tbn
>
>
> 3) I wonder why the Duration is still 00:09:56.52 here ?
>
> ffmpeg -hide_banner -i dv95.dv -r 50 -vf "setpts=0.5*PTS" -an
> dv95_2x_50fps.dv
>
> ffprobe -hide_banner dv95_2x_50fps.dv
>
> [dv @ 0x55fe0b5bb080] Estimating duration from bitrate, this may be
> inaccurate
> Input #0, dv, from 'dv95_2x_50fps.dv':
>   Metadata:
>     timecode        : 00:00:00:00
>   Duration: 00:09:56.52, start: 0.000000, bitrate: 28800 kb/s
>   Stream #0:0: Video: dvvideo, yuv420p, 720x576 [SAR 16:15 DAR 4:3], 28800
> kb/s, 60k fps, 25 tbr, 60k tbn
>
>
> 4)
> ffmpeg -hide_banner -i dv95.dv -f dvd -target pal-dvd -aspect 4:3 -vf
> "setpts=0.5*PTS" -an dv95_2x_25fps.mpg
>
> ffprobe -hide_banner dv95_2x_25fps.mpg
>
> [mpeg @ 0x55a330208080] start time for stream 0 is not set in
> estimate_timings_from_pts
> Input #0, mpeg, from 'dv95_2x_25fps.mpg':
>   Duration: 00:04:58.32, start: 0.540000, bitrate: 6115 kb/s
>   Stream #0:0[0x1bf]: Data: dvd_nav_packet
>   Stream #0:1[0x1e0]: Video: mpeg2video (Main), yuv420p(tv, progressive),
> 720x576 [SAR 16:15 DAR 4:3], 25 fps, 25 tbr, 90k tbn
>     Side data:
>       cpb: bitrate max/min/avg: 9000000/0/0 buffer size: 1835008
> vbv_delay: N/A
> Unsupported codec with id 98312 for input stream 0
>
>
> 5)
> ffmpeg -hide_banner -i dv95.dv -f dvd -target pal-dvd -r 50 -vf
> "setpts=0.5*PTS" -an dv95_2x_50fps.mpg
>
> ffprobe -hide_banner dv95_2x_50fps.mpg
>
> [mpeg @ 0x555e13da2080] start time for stream 0 is not set in
> estimate_timings_from_pts
> Input #0, mpeg, from 'dv95_2x_50fps.mpg':
>   Duration: 00:04:58.26, start: 0.520000, bitrate: 6118 kb/s
>   Stream #0:0[0x1bf]: Data: dvd_nav_packet
>   Stream #0:1[0x1e0]: Video: mpeg2video (Main), yuv420p(tv, progressive),
> 720x576 [SAR 16:15 DAR 4:3], 50 fps, 50 tbr, 90k tbn
>     Side data:
>       cpb: bitrate max/min/avg: 9000000/0/0 buffer size: 1835008
> vbv_delay: N/A
> Unsupported codec with id 98312 for input stream 0
>
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>
> --
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> Cin at lists.cinelerra-gg.org
> https://lists.cinelerra-gg.org/mailman/listinfo/cin
>
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