[FFmpeg-devel] [PATCH] Detect CFR/VFR in libx264.c for proper i_fps_*

Jason Garrett-Glaser jason
Fri Feb 11 21:33:04 CET 2011

On Fri, Feb 11, 2011 at 12:22 PM, Rudolf Polzer <divVerent at alientrap.org> wrote:
> On Fri, Feb 11, 2011 at 09:16:49PM +0100, Rudolf Polzer wrote:
>> This change adds a detection of constant/variable frame rate by the same
>> heuristics as libavformat/utils.c already uses (in performing or refusing
>> frame duration calculation). The heuristics is basically to check whether
>> the time base is larger than 1ms, and assume CFR then, VFR otherwise.
>> Without it, x264 estimates a huge macroblock rate, and thus forces H.264 level
>> 5.1 even if the input could perfectly fine pass as e.g. level 2.1.
> Additional note: the "real" fix to this, long-term, would be an interface
> change to add a VFR flag both to the AVCodecContext and to the AVStream (latter
> being used by libavformat/utils.c's VFR check). However, this should make
> existing libavcodec-using applications work well enough already.
> The x4->params.b_vfr_input does not necessarily need to be handled here, as it
> defaults to 1 and there isn't much disadvantage in setting the flag for CFR
> input according to Dark_Shikari (other than an additional frame of encoding
> latency).

Setting it for *VFR* has little disadvantage.  There's a difference.


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