[FFmpeg-devel] [PATCH v2 2/8] ffmpeg: do packet ts rescaling in write_packet()

[Michael Niedermayer]

On Wed, Feb 15, 2017 at 10:24:17AM +0100, wm4 wrote:
> From: Anton Khirnov <anton at khirnov.net>
> 
> This will be useful in the following commit, after which the muxer
> timebase is not always available when encoding.
> 
> This merges Libav commit 3e265ca. It was previously skipped.
> 
> There is a minor change with setting the mux_timebase field only after
> the muxer's write_header function has been called, because it can
> readjust the timebase.
> 
> Includes a minor merge fix by Mark Thompson, and
> 
>     avconv: Move rescale to stream timebase before monotonisation
> 
> also by Mark Thompson <sw at jkqxz.net>.
> 
> Signed-off-by: wm4 <nfxjfg at googlemail.com>
> ---
>  ffmpeg.c | 39 ++++++++++++++++++++++-----------------
>  ffmpeg.h |  2 ++
>  2 files changed, 24 insertions(+), 17 deletions(-)

Tests run against master with
cb6f1be864c64cfa1d48a5d3eadbecbc771402e7
9148290d71648b0c4295485e59f6541892041a6b
(taken from your git)


This causes a difference in:
./ffmpeg -i ~/tickets/1242/sample.mkv -vcodec copy  -copyts -acodec copy -sn test.ts

Ive looked at the difference and it seems the first timestamp differs
0,      -3780,          0,        0,     3056, 0x00f4902c, S=1,        1, 0x00e000e0
vs.
0,      -3754,          0,        0,     3056, 0x00f4902c, S=1,        1, 0x00e000e0

3754 is closer to 90000/24000/1001
3780 is closer to the first timestamp from the source file

i dont really know what is better

with
./ffmpeg -i ~/tickets/2143/input.mpg -vcodec copy -acodec copy  -ss 7 -t 7 test.mpg

this causes larger timestamp differences and a shower of warnings like
Non-monotonous DTS in output stream 0:0; previous: 483483, current: 483483; changing to 483484. This may result in incorrect timestamps in the output file.

previously no such warnings where generated

with
./ffmpeg -i ~/tickets/2424/aspect_bug.mkv -vcodec copy -acodec copy -t 1 test.mp4
Again the first timestamps change and here also the printed fps value
changes from 24 to 24.01

theres also a differene with Starship_Troopers.vob which i belive i reported
previously

and this also has different timestamps:
./ffmpeg -i ~/tickets/3547/sat_uplink_signalloss.ts -vcodec copy -acodec copy test.asf
interrestingly this is specific to asf output, other formats seem not
to show this

Thats all i could find for the 2 commits with some light analysis.
I Hope it helps

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The misfortune of the wise is better than the prosperity of the fool.
-- Epicurus
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