[mythtv] MPEG4 and seektables

David Asher david.asher at caviumnetworks.com
Fri Mar 17 16:57:36 UTC 2006

I started using Steve Adeff's tv.com script (thanks Steve!) to load some 
videos into the MythTV database.

The are MPEG4 .avi's.  They play fine, but seeking is terrible.  I kinda 
expected that since there was no seek table.

So, I thought: "lets create a seek table for them".  I tried:

$ mythcommflag --rebuild -f <avifile>

This acted like it was working, but the resulting seek table is horribly 

I get all sorts of blocky artifacts (BIG blocks), and when first 
entering the playback after saving position on exit I get a black screen 
which slowly fills in -- sounds like we didn't start on a keyframe?

On starting playback I see (-v playback):

2006-03-16 22:51:40.079 Resyncing position map. posmapStarted = 0 
livetv(0) watchingRec(0)
2006-03-16 22:51:40.096 Position map filled from DB to: 59546
2006-03-16 22:51:40.096 SyncPositionMap prerecorded, from DB: 769 entries
2006-03-16 22:51:40.096 SyncPositionMap, new totframes: 59546, new 
length: 2483, posMap size: 769
2006-03-16 22:51:40.096 AFD: Position map found

on FF I get:

[mpeg4 @ 0x1191a84]warning: first frame is no keyframe

So, I'm thinking the key frames weren't correctly found.

I've got 2 questions:

1. should i expect seek table generation to work for an MPEG4 ?

2. what is the difference between the --video and --rebuild -f options 
for creating the seek table?



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