ylee at pobox
Apr 15, 2007, 8:21 PM
Post #1 of 2
(2318 views)
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What differences do you see between Standard/ffmpeg and libmpeg2?
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I ran into an interesting bug yesterday with an ATSC recording that
always kills mythfrontend, even in the preview window; please see
<URL:http://svn.mythtv.org/trac/ticket/3312> for
details. Interestingly, the bug only occurs when using the Standard
(ffmpeg) decoder, not libmpeg2. I use ATrpms 0.20-155 r13228 (but have
seen the bug at least as far back as 151) with the ffmpeg
0.4.9-19_r7407 and libmpeg2_0-0.4.1-3 (both the latest ATrpms
versions) on a Fedora Core 6 x86_64 distribution running on a Pentium
4 EM64T system.
This brings me to my main question: Just what other differences do
people find between the ffmpeg and libmpeg2 decoders?
Let's first go to what mythfrontend 0.20-fixes says:
* ffmpeg: "Standard will use ffmpeg library." Not much help.
* libmpeg2: "libmpeg2 will use mpeg2 library; this is faster on
some AMD processors."
That description for libmpeg2 sounds intriguing, except that I don't
have an AMD processor. However, could "AMD" here merely be a reference
to the AMD 64-bit extensions which EM64T clones? I wrote almost a year
ago
(<URL:http://www.gossamer-threads.com/lists/mythtv/users/203862#203862>)
that I didn't see a performance difference between the two decoders
when playing back HD video, but that was using a 32-bit version of
Fedora Core 4 on the same hardware. Now, using the same HD recording
as a benchmark for both decoders, I see:
* ffmpeg: 60-70% CPU usage (sometimes dips down to 50%)
* libmpeg2: 40-55% (sometimes spikes up to 60%)
This, plus what I discuss in ticket #3312, would seem to make libmpeg2
the obvious choice for me, except that fast forwarding or rewinding
does not work at any speed above 3X
(<URL:http://www.gossamer-threads.com/lists/mythtv/users/236735#236735>)
when using libmpeg2. (Come to think of it, I should file this as a
ticket, too.) It's not a big deal because I use time skips 99% of the
time anyway. However, that's more because I became used to skipping
instead of fast forwarding/rewinding (as I did with my Series 1 TiVo)
due to this bug.
--
Yeechang Lee <ylee[at]pobox.com> | +1 650 776 7763 | San Francisco CA US
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