no more hslv format ?

[Peter S Kirk]

Many posts back it was mentioned they are not true 50fps, instead each 
frame from a 25fps is duplicated merely to allow BBC to boast about 50fps 
streaming.

On 2 May 2018 at 19:07, Owen Smith Owen Smith <owen.smith at cantab.net> 
wrote:

> What do you mean this isn't a lossy transcoding? How can ffmpeg go from 50fps to 25fps without losing anything? The
> frames are not all complete frames, software can't just throw alternate frames away. Well it could,  but the only way
> to do that is a full H.264 decode, then discard alternate frames, then a full H.264 encode again which is going to
> involve loss.
> 
> Most frames are not fully present in the original stream, they are interpolated from previous and subsequent frames.
> You can't throw any of those away, because other frames are interpolated from them. It would need to be a very special
> original encode which had all even frames only interpolated from other even frames and ditto for odd frames to allow
> alternate frames to be discarded. And a special encode like that would bloat the file size substantially, almost
> doubling it I would expect.