>> Well, it looks like this is because NuppelVideo is one of those horrid
>>variable-FPS file formats; in fact, it makes no attempt whatsoever to keep
>>a constant frame rate!
>>
>Actually, to be fair, Nuppelvideo is probably trying to make the best of
>a bad job. The capture card is a Brooktree BT848 and apart from doing
>PAL-decoding (or NTSC) it does almost nothing other than chuck frames at
>the computer over the PCI bus. I've got a 1600MHz machine, but even then
>it can drop the odd frame here and there.
I can understand where it's coming from, but the logic is still
flawed. The source frames are being generated at a constant frame rate,
25fps (40ms/frame) for PAL; regardless of the exact point in time at which
MythTV picks up the frame, that original interval doesn't change. To give
a graphic, if rather exaggerated, example, this is what MythTV is doing to
the video:
+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
Source | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
+------+------+------+--------+------+------+------+--------+------+
.NUV | 1 | 2 | 3 | 4 | 6 | 7 | 8 | 9 | 11 |
+------+------+------+--------+------+------+------+--------+------+
In other words, each individual frame is being displayed longer than
originally intended, resulting in a slightly slower video that occasionally
"jerks" when frames are dropped due to the time lag. The dropped frames
may be unavoidable, but even then, a proper implementation would generate
something more like:
+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
Source | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
.NUV | 1 | 2 | 3 | 4 | - | 6 | 7 | 8 | 9 | - | 11 |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
where - indicates a dropped frame.
(Incidentally, if your card is dropping frames--as opposed to MythTV
taking too long to encode--you might want to look into getting a new card;
I've got a component capture card that can handle HD video at
[EMAIL PROTECTED] over a standard PCI bus without dropping any frames.)
>Certainly - thanks very much for such a prompt attack on the problem.
>(Or, judging by your website, maybe that should be "domo arigato
>gozaimashita"!)
Douitashimashite. (:
--Andrew Church
[EMAIL PROTECTED]
http://achurch.org/
