On 15/04/18 17:47, Anthony Kehoe wrote:
Thanks, that's useful. -b:v=2285k does indeed give me the bit rate I was
I actually worked on this on Friday. I do a lot of work with ffmpeg to
get encodes working nicely with my 4K telly along with putting things
in iTunes for the AppleTVs.
I added a new option for my copy of get_iplayer, akfps, that changes
the ffmpeg resolutions should a 50fps version be downloaded.
akfps => [ 1, "akfps!", 'Recording', '--akfps', "AK:
Turn on ffmpeg override for 50fps to 25fps conversion"],
Down in sub postproc, I modified the section where @codec_opts builds
the video/audio codec options. I looked at a few BBC encodes and it
seems like they use a bitrate around 2285 with a maxrate of 3500 for
Bit rate mode : Variable
Bit rate : 2 335 kb/s
Maximum bit rate : 3 500 kb/s
Width : 1 280 pixels
Height : 720 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 25.000 FPS
Therefore, I used a target bitrate of 2285 with a maximum of 3500.
For the moment I want to try to reduce the frame rate by dropping
alternate frames as that should avoid any loss of quality in
re-encoding. Also I want to be able to do it in a reasonable time on
this ancient desktop which has a 2.3GHz Core 2 duo.
I gather -r in ffmpeg does not work with -c copy. According to this
article there is a workaround by concatenating a dummy file at the
beginning to set the PTS value. I'll give it a try.
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