[MEncoder-users] Repacking Without Transcoding

[Gordan Bobic]

On 11/03/2014 10:00 PM, Moritz Barsnick wrote:
> Hi Gordon,
>
> mencoder is no longer actively developed, and ffmpeg is recommended as
> a replacement for most use cases. Especially yours. :-)
>
> On Mon, Nov 03, 2014 at 21:16:16 +0000, Gordan Bobic wrote:
>> Unfortunately, the DVDs I've been extracting over time (as the shelf
>> space around the TV has been running out) are mostly in MKV containers
>> with H264 video, which my Chromecasts won't play natively.
>
> I would have expected more from Google, the propagators of WebM, but
> there you go. *shrug*
>
>> What I would ideally like to do is extract the H264 video data and
>> repack it into an MP4 container without transcoding (I don't want to
>> lose any video quality and transcoding is CPU expensive while just
>> re-containering should be much cheaper).
>
> Really easy with ffmpeg:
>
> $ ffmpeg -i infile.mkv -c copy outfile.mp4
>
> is usually all there is to it. If you have more than just one video and
> one audio stream - so for example multiple audio tracks, or subtitle
> streams - you'll have to modify the commandline.
>
> $ ffmpeg -i infile.mkv -sn -c copy -map 0 outfile.mp4
>
> will omit the subtitle streams, but take all available audio (and
> video) streams into the target file.
>
>> Also, in many cases, although the video streams I have been encoding are
>> H264, I have mostly been using MP3 audio rather than AAC, so I will need
>> to transcode the audio.
>
> You should check whether MP3 audio isn't accepted first. Otherwise,
> modify the above to
>
> $ ffmpeg -i infile.mkv -sn -c:v copy -c:a libfdk_aac -map 0 outfile.mp4
>
> or if you don't have libfdk_aac:
>
> $ ffmpeg -i infile.mkv -sn -c:v copy -c:a aac -strict experimental -map 0 outfile.mp4
>
> More help on using ffmpeg here:
> https://ffmpeg.org/mailman/listinfo/ffmpeg-user

Thanks for the hints. I wrote a short script that uses
mplayer -ao null -vo null -really-quiet -identify -frames 1
to get some basic info on the files, and apply transcoding using ffmpeg 
only when necessary.

Thank you again for pointing me in the right direction.

Gordan