The saga continues...
I'm trimming h:\BDMV\STREAM\00305.m2ts, making e:\00305.mkv
FFmpeg appears to be adding soundless audio frames before the 1st video frame.
Concatenating e:\00306.mkv, made the same way, produces stutter & flashing at
the join.
This report concentrates on the '-ss' trim of e:\00305.mkv.
About 00305.m2ts:
The 1st video packet is DTS=1044806, PTS=1048560.
+---------+
... DTS precedes PTS by ¦ 1 frame ¦ <== remember this.
+---------+
--------------------------------+
Now, I want to trim to ¦ 20.061708[3..]..1:33:10.83525 ¦ exactly.
+-------------------------------+
+-------------------------------+
Therefore, I want ¦ PTS=1805553.75..503175172.5 ¦ exactly.
+-------------------------------+
(At least, I think I do.)
'-showinfo' says this:
"n: 481 pts: 1805553 ... type:I".
+-------------------------------+
Therefore, I want frames ¦ 481..134046 ¦ exactly.
+-------------------------------+
But is frame 481 actually at PTS=1805553? No.
Why do I say that? Because '-framecrc' says this:
+-----------------------------------------------+
¦ 1, 1805040, 1805040, 960, 1084 ¦
¦ 1, 1806000, 1806000, 960, 1084 ¦
+-----------------------------------------------+
There is no packet with PTS=1805553 -- doesn't exist.
So, what if I ignore that and just do this:
<windows script>
set SOURCE=h:\BDMV\STREAM\00305.m2ts
set TRIM=-ss 20.061708333333333333333333333333 -to 1:33:10.83525
set ARGS=-map 0 -c copy -dn
set TARGET=e:\00305.mkv
ffmpeg -report %TRIM% -i %SOURCE% %ARGS% %TARGET%
</windows script>
MPV plays it but shows 0:00.616 as the start time.
'-framecrc' shows 43 (presumably soundless) audio packets (DTS=0..448, PTS=0..448) preceding the 1st
video packet (DTS=449, PTS=616).
+----------+
... DTS precedes PTS by ¦ 4 frames ¦
+----------+
The same thing probably happens at the '-to' trim point of 00305.m2ts, and it does happen at the
'-ss' trim point of 00306.m2ts, so when I concat 00305.mkv & 00306.mkv, the join is messed up.
For 2 seconds, MPV stutters 5 times and flashes the first image frame of
00306.mkv 3 times:
stop-pause-go- -stop-pause-go- -stop-flash-pause-go- -stop-flash-pause-go-
-stop-flash-pause-go.
Then MPV continues as though nothing had happened.
Each of the 5 stutters are like micro-movies in which running time stops but
frames 'run'.
Audio & subs flow though all that without a hitch. That tells me that audio packets are actually
'running the show'.
What '-showinfo' is calling "PTS" is not PTS, it's ticks.
Ticks relative to the 1st video packet, but not to _all_ packets.
Since '-showinfo' lies about PTSs, I can't know 'N'.
And 'framecrc' doesn't show 'N's, so I'm in the dark regarding the true identity of the frame and
its true PTS.
I also created e:\00305DTS-STARTDTS÷90.mkv
<windows script>
set SOURCE=h:\BDMV\STREAM\00305.m2ts
set TRIM=-ss 20.061708333333333333333333333333 -to 1:33:10.83525
set BSFV=-bsf:v setts=dts=DTS-STARTDTS/90:pts=PTS-STARTPTS/90
set BSFA=-bsf:a setts=dts=DTS-STARTDTS/90:pts=PTS-STARTPTS/90
set ARGS=-map 0 %BSFV% %BSFA% -c copy -dn
set TARGET=e:\00305_DTS-STARTDTS÷90.mkv
ffmpeg -report %TRIM% -i %SOURCE% %ARGS% %TARGET%
</windows script>
and got similar results.
I'm like you. I just want perfect video. I'll really appreciate help.
-- Mark.
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