[mythtv-users] "mythtranscode --mpeg2" and Vertical Purple Lines

Dave Sp davespmyth at gmail.com
Thu Nov 3 00:13:21 UTC 2011

On Wed, Oct 12, 2011 at 6:05 AM, Dave Sp <davespmyth at gmail.com> wrote:

> On Mon, Oct 10, 2011 at 5:11 AM, Dave Sp <davespmyth at gmail.com> wrote:
>> On Fri, Oct 7, 2011 at 6:08 PM, James MacKenzie <mst3000 at newsguy.com>wrote:
>>> Have you tried playing the file on another device?
>>> The reason I ask is that I had an issue with vertical purple lines on
>>> playback of mpeg2 on anything 1280x720 or 1920x1080 at one point.  I had to
>>> adjust my playback profile and then everything played fine.
>>> Not sure it is your problem, but thought I'd mention it.  If you aren't
>>> normally playing things in mpeg2 this might be your issue.
>>> ------------------------------
>>> *From:* Dave Sp <davespmyth at gmail.com>
>>> *Sent:* Fri, 7 Oct 2011 16:47:40 -0400 (EDT)
>>> *To:* Discussion about mythtv <mythtv-users at mythtv.org>
>>> *Subject:* [mythtv-users] "mythtranscode --mpeg2" and Vertical Purple
>>> Lines
>>>  I use "mythtranscode --mpeg2 --honorcutlist ..." from the command line
>>> to create a cut version of a recording.
>>> When I play the result, vertical purple lines show up a couple every 50
>>> seconds.  Each burst of purple lines lasts 20 frames, give or take a few.
>>> (If I don't use the "--mpeg2" option, the result has no purple lines,
>>> but it takes a lot longer to generate the file.)
>>> Any idea what could be causing this?
>>> --Dave
>> The output from "mythtranscode --mpeg ..." has those purple vertical
>> lines when played in mythvideo, mplayer, and even vlc.
>> I re-ran "mythtranscode --mpeg ..." with "-v all".  It seems the purple
>> lines coincide with the debug lines "Inserting 0 I-Frames after #....".
>> Is inserting "0" I-frames causing the glitches?
>> --Dave
> Each time MPEG2fixup::Start had to call InsertFrame, deltaPTS was either
> 1201 or 1202, and ptsIncrement was 1501.  If I prevent calling InsertFrame
> under those conditions, the end result has no vertical line artifacts every
> 50 seconds, but then handbrake-cli spits out hundreds of "sync: video time
> didn't advance" messages and mythvideo complains of lots of A/V sync issues
> and doesn't show the time properly.
> So it seems InsertFrame needs to be called when deltaPTS is either 1201 or
> 1202 and ptsIncrement is 1501.  Is MPEG2fixup::InsertFrame supposed to
> insert a duplicate of the previous frame, or is it inserting a frame with
> no data (resulting in those vertical-line artifacts)?

Follow-up:  After a recent ffmpeg/libav* package upgrade from
debian-multimedia.org, my "purple vertical lines" issue has disappeared. (I
used the same source recording to verify that the issue is gone.)  I didn't
have to re-compile Myth for this to happen.

I'm not sure (yet) what the external bug was.  If I do find out, I'll
update this thread (just in case anyone else is curious).

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