Problem with get_position and get_length on transport stream

[slasktrat]

Hi

I use vlc as PVR for dumping multicast TV to .ts files. Sometimes i start playback of the recording before the program has ended. In earlier versions of VLC the libvlc_media_player_get_position and libvlc_media_player_get_length would always give me correct result, even as the source file grows. But now (don't know which version of vlc that changed this behaviour) libvlc_media_player_get_length will always return the lenght that the video had when the playback started, and libvlc_media_player_get_position will en up returning a float larger than 1 when passing initial lenght.

Is there a good reason why this no longer works as before? And is there any other way i can get libvlc to give me updated lenght and pos as the source grows?


Thanks

[maharg]

This is an issue I'll be interested in also.

A thought regarding a possible workaround - it should be possible to approximate the position given the original file size, the current file size, and the mis-reported position.

[maharg]

I've recreated this using the Python bindings to libvlc as shown below.

The file which is being played back is being captured using multicat, and is growing (confirmed with watch ls -l ....).

Notes:
- The output from VLC is left intact. I didn't create a context for the player so only the audio was rendered, but this was sufficient for the test.

Findings:
- get_position reports positions > 1.0 when playback passes the original duration of the file
- it is NOT possible to set a position > 1.0 - VLC simply plays from position 1.0
- get_length consistently reports the original length of the clip

Code: Select all

$ export VLC_PLUGIN_PATH=/Applications/VLC.app/Contents/MacOS/plugins/ $ python Python 2.7.5 (default, Mar 9 2014, 22:15:05) [GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.0.68)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import vlc >>> instance = vlc.Instance() >>> player = instance.media_player_new() >>> media = instance.media_new("file:///Volumes/captures/bbcnew_1_1466406091/407336.ts") >>> player.set_media(media) >>> player.play() 0 >>> [00007fc802f544c8] macosx vout display error: No drawable-nsobject nor vout_window_t found, passing over. [00007fc80389deb8] core video output error: video output creation failed [00007fc8030a62b8] core decoder error: failed to create video output >>> vlc.libvlc_media_player_get_position(player) 0.10156689584255219 >>> vlc.libvlc_media_player_get_length(player) 1176666 >>> vlc.libvlc_media_player_get_length(player) 1176666 >>> vlc.libvlc_media_player_get_length(player) 1176666 >>> vlc.libvlc_media_player_get_length(player) 1176666 >>> vlc.libvlc_media_player_get_length(player) 1176666 >>> vlc.libvlc_media_player_get_length(player) 1176666 >>> vlc.libvlc_media_player_get_length(player) 1176666 >>> vlc.libvlc_media_player_get_length(player) 1176666 >>> import time >>> while True: ... vlc.libvlc_media_player_get_position(player) ... time.sleep(1) ... 0.2612680494785309 0.262220561504364 0.2629339098930359 0.26387032866477966 0.26477792859077454 0.26570072770118713 0.2663840651512146 0.26731234788894653 0.2681690752506256 0.268882691860199 0.2698352336883545 0.27076664566993713 0.271470308303833 0.2724232077598572 0.2733567953109741 ^CTraceback (most recent call last): File "<stdin>", line 3, in <module> KeyboardInterrupt >>> vlc.libvlc_media_player_set_position(player, .98) >>> [00007fc802d78ca8] ts demux error: libdvbpsi error (PSI decoder): TS discontinuity (received 4, expected 13) for PID 0 [00007fc802d78ca8] ts demux error: libdvbpsi error (PSI decoder): TS discontinuity (received 0, expected 9) for PID 500 [00007fc802d78ca8] ts demux error: libdvbpsi error (PSI decoder): TS discontinuity (received 10, expected 1) for PID 17 [00007fc802d78ca8] ts demux error: libdvbpsi error (PSI decoder): TS discontinuity (received 8, expected 2) for PID 20 >>> >>> while True: ... vlc.libvlc_media_player_get_position(player) ... time.sleep(1) ... 0.9883562326431274 0.9893091917037964 0.9900230169296265 0.9909444451332092 0.9918898940086365 0.9927594661712646 0.9932050704956055 0.9943660497665405 0.9952577352523804 0.9959721565246582 0.9968942999839783 0.9978464245796204 0.9985599517822266 0.999513566493988 1.0004348754882812 1.0011491775512695 1.002070426940918 1.0027828216552734 ^CTraceback (most recent call last): File "<stdin>", line 3, in <module> KeyboardInterrupt >>> vlc.libvlc_media_player_set_position(player, 1.05) >>> [00007fc802d78ca8] ts demux error: libdvbpsi error (PSI decoder): TS discontinuity (received 8, expected 7) for PID 0 [00007fc802d78ca8] ts demux error: libdvbpsi error (PSI decoder): TS discontinuity (received 4, expected 3) for PID 500 [00007fc802d78ca8] ts demux error: libdvbpsi error (PSI decoder): TS discontinuity (received 1, expected 14) for PID 17 vlc.while True: ... vlc.libvlc_media_player_get_position(player) ... time.sleep(1)[00007fc802d78ca8] ts demux error: libdvbpsi error (PSI decoder): TS discontinuity (received 10, expected 11) for PID 20 ... 1.0063832998275757 1.0073349475860596 1.0080195665359497 1.0088791847229004 1.0098339319229126 1.0105475187301636 ^[[A^[[A1.0114997625350952 ^CTraceback (most recent call last): File "<stdin>", line 3, in <module> KeyboardInterrupt >>> vlc.libvlc_media_player_set_position(player, 1.4) >>> [00007fc802d78ca8] ts demux error: libdvbpsi error (PSI decoder): TS discontinuity (received 6, expected 9) for PID 0 [00007fc802d78ca8] ts demux error: libdvbpsi error (PSI decoder): TS discontinuity (received 2, expected 5) for PID 500 [00007fc802d78ca8] ts demux error: libdvbpsi error (PSI decoder): TS discontinuity (received 1, expected 8) for PID 17 vlc. KeyboardInterrupt >>> >>> >>> >>> while True: ... vlc.libvlc_media_player_get_position(player)[00007fc802d78ca8] ts demux error: libdvbpsi error (PSI decoder): TS discontinuity (received 10, expected 11) for PID 20 ... time.sleep(1) ... 1.0086743831634521 1.009626030921936 1.0105475187301636 1.0112614631652832 1.0121963024139404 1.0128976106643677 1.013848900794983 ^CTraceback (most recent call last): File "<stdin>", line 3, in <module> KeyboardInterrupt >>> vlc.libvlc_media_player_get_position(player) 1.0611735582351685 >>> vlc.libvlc_media_player_get_position(player) 1.0630782842636108 >>> vlc.libvlc_media_player_get_position(player) 1.0640308856964111 >>> vlc.libvlc_media_player_set_position(player, 1.06) >>> [00007fc802d78ca8] ts demux error: libdvbpsi error (PSI decoder): TS discontinuity (received 1, expected 15) for PID 17 [00007fc802d78ca8] ts demux error: libdvbpsi error (PSI decoder): TS discontinuity (received 10, expected 15) for PID 0 [00007fc802d78ca8] ts demux error: libdvbpsi error (PSI decoder): TS discontinuity (received 6, expected 11) for PID 500 vlc.libvlc_media_player_set_get_position(player) 1.0034089088439941 >>> [00007fc802d78ca8] ts demux error: libdvbpsi error (PSI decoder): TS discontinuity (received 10, expected 0) for PID 20

[maharg]

Tried again with latest nightly (vlc-3.0.0-20160620-0441-git)

Notes:
- had to specify option --no-video to get the playback to work

Findings:
- get_length doesn't reflect current duration of file as it grows
- get_position reports position > 1.0 as playback passes the original duration i.e. the duration when the file was opened
- set_position can be set to a value >1.0 but doing so results in playback stopping, and get_position then returns the same (~ floating point precision) value repeatedly.

Code: Select all

$ python Python 2.7.5 (default, Mar 9 2014, 22:15:05) [GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.0.68)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import vlc >>> instance = vlc.Instance(['--no-video']) >>> player = instance.media_player_new() >>> media = instance.media_new("file:///Volumes/captures/bbcnew_1_1466406091/407338.ts") >>> player.set_media(media) >>> player.play() 0 >>> >>> >>> >>> vlc.libvlc_media_player_get_length(player) 343976 >>> vlc.libvlc_media_player_get_length(player) 343976 >>> vlc.libvlc_media_player_get_length(player) 343976 >>> vlc.libvlc_media_player_get_length(player) 343976 >>> vlc.libvlc_media_player_get_position(player) 0.06074704974889755 >>> vlc.libvlc_media_player_get_position(player) 0.06123490631580353 >>> vlc.libvlc_media_player_get_position(player) 0.0760301873087883 >>> vlc.libvlc_media_player_get_position(player) 0.07885760813951492 >>> vlc.libvlc_media_player_get_position(player) 0.08091051876544952 >>> vlc.libvlc_media_player_get_position(player) 0.0860622301697731 >>> vlc.libvlc_media_player_get_position(player) 0.09124723076820374 >>> vlc.libvlc_media_player_set_position(player, .98) >>> vlc.libvlc_media_player_get_position(player) 1.183619499206543 >>> vlc.libvlc_media_player_get_position(player) 1.1918147802352905 >>> vlc.libvlc_media_player_set_position(player, 1.18) >>> vlc.libvlc_media_player_get_position(player) 1.1799999475479126 >>> vlc.libvlc_media_player_get_position(player) 1.1799999475479126 >>> vlc.libvlc_media_player_get_position(player) 1.1799999475479126 >>> vlc.libvlc_media_player_get_position(player) 1.1799999475479126 >>> vlc.libvlc_media_player_get_position(player) 1.1799999475479126 >>> vlc.libvlc_media_player_get_position(player) 1.1799999475479126 >>> vlc.libvlc_media_player_get_position(player) 1.1799999475479126 >>> player.play() 0 >>> vlc.libvlc_media_player_get_position(player) 1.1799999475479126 >>> vlc.libvlc_media_player_get_position(player) 1.1799999475479126 >>>

[maharg]

I have now raised this on the trac at https://trac.videolan.org/vlc/ticket/17085

[maharg]

Fixed in 3.0.0 FF - commit at https://github.com/videolan/vlc/commit/ ... bd02447fd6

[Jean-Baptiste Kempf]

Nice