[mythtv-users] Converting MythTV Frame/time to ffmpeg time?

[John Pilkington]

On 25/01/16 07:51, Philipp Hahn wrote:
> Hello,
>
> I have several recordings from DVB-C (Europe/Germany, so PAL with 720p,
> 50Hz) already with H.264, which MythTranscode refuses to cut losslessly.
> I normally start my recordings 2 minutes early and let it record 5
> minutes after the scheduled end to not miss anything.
> I now try to remove those extra seconds to save space.  I've then set
> two cut points to cut the beginning and ending.
>
> As MythTranscode refuses to cut H.264 itself (`mythtranscode --mpeg2
> --honorcutlist` errors out with 'no more queue slots' or other error
> messages), it seems I have to do it myself using ffmpeg directly. Bug I
> can't convert the MythTV frame number or time stamp to something ffmpeg
> understand or is exact. There also seems to be different values for the
> end:
>
> # chanid="13120"
> # starttime="20150715225300"
> # mythutil -q --chanid "$chanid" --starttime "$starttime" --getcutlist
> Cutlist: 0-12129,175474-185836
>
> If I open the cut-list editor in the frontend and go to the very end, I
> get a different frame number:
>
> Frame   Time
>       1    00:00:021
>   12129    04:02.600
> 175474    58:29.500
> 185776  1:01:55.540
> ^^^^^^ At least the last one is different from the output of
> --getcutlist above?
>
> If I directly look at the SQL tables, I get yet another set of values:
>
> mysql> SELECT * FROM recordedmarkup WHERE starttime="20150715225300" AND chanid="13120";
> +--------+---------------------+--------+------+---------+
> | chanid | starttime           | mark   | type | data    |
> +--------+---------------------+--------+------+---------+
> |  13120 | 2015-07-15 22:53:00 |  12129 |    0 |    NULL |
> 0=MARK_CUT_END
> |  13120 | 2015-07-15 22:53:00 |      1 |   12 |    NULL |
> 12=MARK_ASPECT_16_9
> |  13120 | 2015-07-15 22:53:00 |      1 |   30 |    1280 |
> 30=MARK_VIDEO_WIDTH
> |  13120 | 2015-07-15 22:53:00 |      1 |   31 |     720 |
> 31=MARK_VIDEO_HEIGHT
> |  13120 | 2015-07-15 22:53:00 |      1 |   32 |   50000 |
> 32=MARK_VIDEO_RATE: 50 Hz
> |  13120 | 2015-07-15 22:53:00 |      0 |   33 | 3720000 |
> 33=MARK_DURATION_MS: 3729.000s = 1:02:00.000
> |  13120 | 2015-07-15 22:53:00 |      0 |   34 |  185785 |
> 34=MARK_TOTAL_FRAMES: yet another value?
> |  13120 | 2015-07-15 22:53:00 |      0 |   -3 |    NULL |
> -3=MARK_UPDATED_CUT
> |  13120 | 2015-07-15 22:53:00 |   7014 |    4 |    NULL |
> |  13120 | 2015-07-15 22:53:00 |  12126 |    5 |    NULL |
> |  13120 | 2015-07-15 22:53:00 | 175468 |    4 |    NULL |
> |  13120 | 2015-07-15 22:53:00 | 186260 |    5 |    NULL |
> 4=MARK_COMM_START
> 5=MARK_COMM_END
> |  13120 | 2015-07-15 22:53:00 | 175474 |    1 |    NULL |
> 1=MARK_CUT_START
> +--------+---------------------+--------+------+---------+
> 13 rows in set (0.00 sec)
>
>
> mysql> SELECT * FROM recordedseek WHERE starttime="20150715225300" AND chanid="13120" LIMIT 0,10;
> +--------+---------------------+------+---------+------+
> | chanid | starttime           | mark | offset  | type |
> +--------+---------------------+------+---------+------+
> |  13120 | 2015-07-15 22:53:00 |    0 |       0 |    9 |
> |  13120 | 2015-07-15 22:53:00 |   32 |  378444 |    9 |
> |  13120 | 2015-07-15 22:53:00 |   64 |  622092 |    9 |
> |  13120 | 2015-07-15 22:53:00 |  100 |  940752 |    9 |
> |  13120 | 2015-07-15 22:53:00 |  136 | 1305096 |    9 |
> |  13120 | 2015-07-15 22:53:00 |  168 | 1673952 |    9 |
> |  13120 | 2015-07-15 22:53:00 |  200 | 2103156 |    9 |
> |  13120 | 2015-07-15 22:53:00 |  232 | 2615456 |    9 |
> |  13120 | 2015-07-15 22:53:00 |  264 | 3061580 |    9 |
> |  13120 | 2015-07-15 22:53:00 |  296 | 3604336 |    9 |
> +--------+---------------------+------+---------+------+
> 10 rows in set (0.01 sec)
> mysql> SELECT * FROM recordedseek WHERE starttime="20150715225300" AND chanid="13120" LIMIT 11480,10;
> +--------+---------------------+--------+---------+------+
> | chanid | starttime           | mark   | offset  | type |
> +--------+---------------------+--------+---------+------+
> |  13120 | 2015-07-15 22:53:00 | 185744 | 3714900 |   33 |
> |  13120 | 2015-07-15 22:53:00 | 185776 | 3715540 |   33 |
> +--------+---------------------+--------+---------+------+
> 2 rows in set (0.02 sec)
>
>
> So how does one convert the MythTV values to something I can pass to
> ffmpeg to get the exact cut points?
> My tries with frame * 1s/50 have failed so far, which leads to the
> output file to still start with some frames before or after the exact
> frame, etc.
>
> Thanks in advance.
> Philipp
>

I haven't tried using ffmpeg to cut h264, but your use-case sounds as if 
my mythDVBcut script could fit - or at least give you a possible 
starting point.  For non-mpeg2 recordings it just cuts at 
video-keyframes, with no demux/remux complications.  It works with DVB-T 
radio as well, with 1-sec granularity.

https://www.mythtv.org/wiki/MythDVBcut

HTH

John P