[x264-devel] Changing bitrate on the fly

[Jason Garrett-Glaser]

On Thu, Dec 17, 2009 at 4:02 AM, Arindam Biswas <send2ari at gmail.com> wrote:
> Hi,
> Is there any way/patch to change bitrate on the fly during encoding? I am
> working on a network application where I am continuously changing the
> bitrate based on network condition.
> After searching through the mailing list I found that stopping and starting
> the encoder is the best way. But I have a problem with that solution.
> Because starting the encoder means one IDR frame is inserted which means
> more bits so it is working worse when the network has significant amount of
> loss.

Patches welcome, but this would require significant modifications to
VBV in addition to the rest of ratecontrol.

> My second question is I am working on a transcoding application where I am
> getting h.264 stream, for changing the bitrate of stream by decoding and
> encoding with new rate. It is taking huge CPU.
> Can we do something like h.264 stream-->entropy
> decoding-->dequantization->requantization->entropy->h.264 stream.

This won't work due to the fact that intra prediction is IIR.  You
need to perform inverse transform and prediction too, at which point
you're basically re-encoding.

> I like know if this kind of technique is already implemented in any open
> source?. If not then can u give me some guideline of how to implement it
> using ffmpeg (h.264 decoder) and x264(h.264 encoder)?

Guideline: Don't even bother.

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