HDTV at greater than 1.0 speed stutters

[jppoet@…]

By simply changing the readblocksize in RingBuffer?.cpp, I can now watch HD programs at up to 1.2x speed without it stuttering.

Unfortunately, 1.2x is as fast as I can go before the stuttering returns.

Patch is attached.

John

[jppoet@…]

Modify readblocksize for smoother playback.

[danielk]

John I don't want to commit this before 0.19 because RingBuffer::CalcReadAheadThresh?() changes tend to break things, but I will commit something similar that should allow > 1.2 playback as well by adjusting the buffering for faster playback.

I think this change, as is, could further break smooth ringbuffer switching.

[danielk]

(In [8841]) Fixes #971. Fixes #900.

In SwitchToProgram?() we check if we close to the end before doing a switch. This was safe for low bitrate programs, but with high bitrate programs the RingBuffer? was initialized with a larger readblocksize. Also the valid video frames check isn't terribly valid with nVidia XvMC, which uses a total of only 8 video buffers.

This reworks this check and moves it to NVP::IsReallyNearEnd?(). It uses information from the RingBuffer? to set the thresholds so it scales with different bitrates. Also, the ringbuffer now takes the play_speed into account when using timestretch. The raw bitrate as reported by ffmpeg is scaled by timestretch value. Also since IsReallyNearEnd?() is using the real readblocksize in it's calculations, I've applied John Poet's patch for making 1080i @ >=1.2 timestretch work by increasing the readblocksize.

The params may need some tuning for the best performance. The values I used are both theoretically safe and worked for the 400 ringbuffer switches I threw at it. But the params are somewhat conservative. When I used the theoretical minimums, I did observe a lockup after about 70 switches, so my model isn't perfect.