no more hslv format ?

[Owen Smith]

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.

-- 
Owen Smith <owen.smith at cantab.net>
Cambridge, UK

> On 2 May 2018, at 16:20, Ralph Corderoy <ralph at inputplus.co.uk> wrote:
> 
> Hi Jim,
> 
>>> You could use get_iplayer's --command option to run a command to
>>> move each final file off tmpfs as the download is finished.  Its
>>> --output affects all the intermediate files too, AIUI.
>> 
>> The challenge for me is to work out how to get the fetched file to go
>> onto the tmpfs
> 
> Well, `df -t tmpfs' will probably show /tmp is a tmpfs so you could
> `--output /tmp' and you should see its intermediate files, and the final
> file, only appear there.  `--command' could then move that final file to
> the SSD, or run a conversion command that writes to the SSD and then
> removes the tmpfs input.
> 
> As for altering the ffmpeg command that get_iplayer is using, I'm not
> sure that's worthwhile?  It isn't doing any transcoding, just changing
> the container format, or splicing in better audio, that kind of thing.
> So your `lossy' slow-down ffmpeg from 50 fps to 25 fps won't be a second
> lossy one that you'd prefer to combine with the first.  I could be
> wrong, not knowing how to have ffmpeg do this conversion.  When you find
> out, let the list know.  :-)
> 
> -- 
> Cheers, Ralph.
> https://plus.google.com/+RalphCorderoy
> 
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