[Ffmpeg-devel] Re: [Ffmpeg-user] ffmpeg encoding, reallyslowvideo when recording with audio (original) (raw)

Erik Slagter erik
Fri Feb 3 19:14:19 CET 2006

On Fri, 2006-02-03 at 15:53 +0100, Luca Abeni wrote:

> The saa7134 (on which the cinergy cards are based) delivers both video > and audio, the latter one via it's own, more or less oss compatible > interface. Ah, ok... I misunderstood you. I am capturing audio through a "regular" audio card (using oss emulation over alsa).

Yes, I know :-) bt848/bt878. The bt878 also offers audio but it seems not many people get it working.

In case I get a saa7134-based card, how can I setup the drivers to capture both video and audio from the card, so that I can reproduce the bug?

Completely default. If you have a cinergy card with a broken crystal, you'll know very soon :-(

> If everything is alright, it will try and succeed in keeping > audio and video in sync; it is able to vary the samplerate of the audio > slightly to compensate for drifts, which works very nicely. But if the > crystal is wrong, it doesn't work. If the audio coming from the card is available through the OSS interface, I think libavformat will associate timestamps to it based on gettimeofday(), and ffmpeg will do the samplerate adjustments by resampling the audio (if you specify the async option). So, I suspect ffmpeg can work around this hw/driver's bug. But I am just speculating ;-)

Hmmm, I doubt that ffmpeg can work around the "smartness" of the saa7134, which, in this case, is counterproductive.

Does alsa provide timestamps? (BTW, what about explicit alsa support in libavformat? No, I will not have time for working on it, but if someone else steps in... ;-)

Hmmm, ffmpeg alsa support for ffmpeg, that would be interesting. I don't know if alsa supports timestamps, but there will undoubtedly be more something like timing info. -------------- next part -------------- A non-text attachment was scrubbed... Name: smime.p7s Type: application/x-pkcs7-signature Size: 2771 bytes Desc: not available URL: <http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/attachments/20060203/a614c747/attachment.bin>

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