[FFmpeg-user] HLS program-date-time drifts

[Chris Hiszpanski]

Hello,

I am using the HLS plugin, which is generating a .m3u8 playlist and its corresponding MPEG-2 transport stream segments:

I'm noticing that if I leave this running for multiple days, the datetime in `EXT-X-PROGRAM-DATE-TIME` drifts from the actual clock time of the system, readily apparent because the segments are named in `YYYY_mm_DD__HH_MM_SS.ts` format (the .ts names match the system `date`). Here is how I am running ffmpeg (`ffmpeg version 3.4.1-static https://johnvansickle.com/ffmpeg/`):

    ffmpeg -re -r 36 -f h264 -i /var/run/my_named_pipe.h264 -vcodec copy -an -r 36 -use_localtime 1 -f hls -flags +cgop -g 25 -hls_time 6 -hls_list_size 5 -hls_start_number_source datetime -hls_allow_cache 1 -hls_flags program_date_time -hls_segment_filename http://localhost/%Y_%m_%d__%H_%M_%S.ts -method PUT http://localhost/myfeed.m3u8

My hardware generates a 36 frames-per-second h.264 byte stream (baseline profile, with 25 frame group-of-pictures) and writes it to a named pipe, from which ffmpeg reads. Here is the m3u8 that shows the issue:

```m3u8
    #EXT-X-VERSION:3
    #EXT-X-MEDIA-SEQUENCE:0
    #EXT-X-TARGETDURATION:7
    #EXT-X-PROGRAM-DATE-TIME:2018-01-23T15:03:35-08:00
    #EXTINF:6.250,
    2018_01_23__15_04_33.ts
    #EXT-X-PROGRAM-DATE-TIME:2018-01-23T15:03:41.25-08:00
    #EXTINF:6.250,
    2018_01_23__15_04_39.ts
    #EXT-X-PROGRAM-DATE-TIME:2018-01-23T15:03:47.5-08:00
    ...
```

Notice how the datetimes differ by almost a minute. These were the same value some 24 hours ago.

Is this a bug, or am I missing something?

Thanks,
Chris