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

Dave Sp davespmyth at gmail.com
Wed Oct 12 11:05:05 UTC 2011

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)?

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