VLC sets an incorrect mux_rate when creating PS files

Seems the calculation of timing info for MPEG2-PS files is inaccurate.

File with length of 1 min 11 seconds is reported as being only 37 seconds long. During playback, the time counter increments in about 2 sec. intervals.

changed milestone to %0.8.5-test3

Regarding the PowerDVD example, this ticket seems to describe same issue as #198 (closed) which has details.

Original author: tumu

added Status::duplicate label

closed

No, I'm not reffering to any DVDs, nor DVD files (.vob). This file is plain MPEG-2 PS with constant bitrate (recorded from a TV station and saved in PS format by VLC).

Something's wrong in PS demuxer calculations.

The dvdread/dvdnav modules mentioned in #198 (closed) are not being used in this case

removed Status::duplicate label

reopened

All my CBR MPEG-PS samples are correct. If there is an issues, you should upload the file to the FTP, so it can be investigated.

OK, it's there - ftp://streams.videolan.org/incoming/test.mpg

Real length is 30 seconds.

Also see #216 (closed). Should the various tickets be merged?

Original author: tumu

If this is actually a bug in reading PS CBR files, then it's a separate bug.

This is the corresponding code block in modules/demux/ps.c

          *pi64 = (int64_t)1000000 * ( stream_Tell( p_demux->s ) / 50 ) /
                p_sys->i_mux_rate;

What is the meaning of the constant 50 here? Shouldn't we read the actual framerate from the stream? This would be 25 as this is PAL TV with 50 half-frames (fields).

the meaning of the constant 50 is as follows:

the i_mux_rate is the mux_rate value as specified in the PACK header. PACK specifies this value as: The multiplied bitrate in units 50Bytes / second

Your specific clip specified 25200 units == 1260000 bytes/s == 10080000 bits/s

Now either VLC retrieves an incorrect MUX rate, or an incorrect MUX rate is being written.

changed title from Timing information for MPEG2 PS files incorrect to VLC sets an incorrect mux_rate when creating PS files

changed the description

I looked at the file in quite some detail, investigated VLCs PACK header reading, and as far as I can tell, the mux_rate is simply set incorrectly in this file.

That still leaves the issue that we shouldn't be using the mux_rate in the first place of course, but that already has ticket #216 (closed).

BTW: other players probably don't base their estimate on the mux rate, but rather on the first and last PTS in the file. explaining why only VLC is seeing this issue.

added Component::Stream output: Muxers label

changed milestone to %0.8.5-final

changed milestone to %0.8.6 maintenance

changed milestone to %Bugs paradize