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

[Terje J. Hanssen]

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?


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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