[mythtv] mythvideo ffw/rwd not smooth and sound disable

Martin Long mythtv at longhome.co.uk
Sun May 27 11:04:23 UTC 2007

I don't quite know what your perception of 'jumping' or 'not smooth' is, but
typically ffwd or rew of any mpg (or any compressed) stream will appear to
jump - this is because the CPU would be incapable of decoding the mpg stream
fast enough to show every frame, (it would have to at least process every
frame, even if it only shows every other, third, forth etc, as the
contruction of many frames relies on the last, or next frame being
complete). So, in order to allow fast forwarding, and provide a decent
visual queue, only keyframes (those which are stored as complete frames) are
decoded. This makes the experience seem jumpy, but it is unavoidable. How
jumpy it is depends on the keyframe ratio of the content (which would
typically depend on the encoding rate, DVDs would have a higher keyframe
rate than DVB broadcasts for example) Unless you are having other
performance issues which are having an even more detrimental effect on ffwd
/ rew, then I doubt disabling the sound would effect this. Decoding small
chunks of sound is relatively inexpensive wrt CPU time, and playing is
virtually free (you load up the buffer, and the hardware takes care of the



From: mythtv-dev-bounces at mythtv.org [mailto:mythtv-dev-bounces at mythtv.org]
On Behalf Of Bill
Sent: 27 May 2007 01:23
To: mythtv-dev at mythtv.org
Subject: [mythtv] mythvideo ffw/rwd not smooth and sound disable


For mpg files, the internal player will play sound bites as it fast forwards
or rewinds.  I would like to provide an option to disable this in the code.
Can someone point me in the right direction in the code?  I haven't been
able to find it yet, found where the ffw/rwd occurs but haven't figured out
the sound part yet.


I find that ffw/rwd is not smooth at all, very jumping, hoping disabling the
sound will fix this as I see lots of "NVP::AddAudioData():p1: Audio buffer
overflow, audio data lost!"  Besides I don't want the sound anyway.


Also TV recordings and DVD images (ISO) are smooth on ffw/rwd; there is no
sound during ffw/rwd also no sound error messages.  I have not been able to
find in the in the code why there would be sound for mpg but not for other


Any help would be appreciated

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