prevailing best method for converting .mp4/avc&aac into .mkv/avc&mp3 ?

[hydra3333]

I just bought a "Fetch TV" PVR (Australia) https://www.fetchtv.com.au/ and subscribed to a cheapie subscription pack, since I can't afford Foxtel any more (it's very expensive).

Anyway, this thing apparently only plays a limited selection of file types from USB and home media servers, mainly MKV files containing mpeg4&mp3 or mpeg2&mp3. No MP4/avc&aac. Not the greatest format/codec support, but there it is, and it is the only alternative in Australia which offers subscriptions to some UK channels (they have great crime/detective shows from time to time).

I have lots and lots of home movies and whatnot in mp4/avc&aac (most interlaced, 1080i and 576i, a fair number 576p). Many of the videos have various audio offsets.

Hence, what in your view is the prevailing latest and greatest method to convert the .mp4 files into mkv/avc&mp3 or mkv/mpeg2&mp3 without lip sync issues etc ?

My initial guess would be via ffmpeg using say -c:v copy and -c:a libmp3lame -ab 384k and -y output_file.mkv which avoids transcoding the video ?

[netmask56]

The quickest way to is to try MKVToolNix to put you files in a MKV container and see if they play in your device - it doesn't re-encode so is quick but wouldn't change the audio to a preferred format so probably ffmpeg is the best bet.

[sneaker]

My initial guess would be via ffmpeg using say -c:v copy and -c:a libmp3lame -ab 384k and -y output_file.mkv which avoids transcoding the video ?

Looks good (common mp3 bitrate limit is 320k, though). Why don't you test it? There are so many different devices with so many different requirements that testing yourself is pretty much the only thing you can do. (If simple remux like netmask56 works: even better)

Note: "mpeg4" can mean different things. mpeg-4 part 10 is H.264/AVC, mpeg-4 part 2 is the old DivX/XviD thing.

[pandy]

I would go for quality not bitrate - -q:a 0 should work very nice for libmp3lame.

[hydra3333]

OK and thanks. Testing it is, then.

-q:a 0 does sound attractive, however I wonder in this case
https://trac.ffmpeg.org/wiki/Encode/MP3

-q:a 0 (NB this is VBR from 22 to 26 KB/s)

... the incoming audios range around 224k to 384k ...

and
https://trac.ffmpeg.org/wiki/Encode/MP3

-b:a 320k (NB this is 32KB/s, or its max)

which I suppose means I'm limited to 320k for mp3 ?

[mail2tom]

According to the specs sheet you should be able to re-wrap your files into a TS transport stream file using tsmuxer. That container seems to be the most flexible and allows for a variety of different audio and video format.

[hydra3333]

According to the specs sheet you should be able to re-wrap your files into a TS transport stream file using tsmuxer. That container seems to be the most flexible and allows for a variety of different audio and video format.

Thank you. Yes you are right, the spec appendix does say that.
I'd ignored .TS as a container without critical thinking, because everywhere you look people are talking about converting to use .mp4 and .mkv containers and not .ts. I now wonder why.

I googled to find pros and cons of .MKV vs .TS and saw not a lot.

https://en.wikipedia.org/wiki/Comparison_of_video_container_formats which says

MPEG transport stream TS (.ts) MPEG Patent encumbered

https://en.wikipedia.org/wiki/MPEG_transport_stream

because of the tiny packet size, streams can be interleaved with less latency and greater error resilience compared to program streams and common containers such as AVI, MOV/MP4, and MKV, which generally wrap each frame into one packet.

As far as I can tell, there's not much else in the way of describing under what circumstances to use one over the other (apart from .ts is intended for broadcast and is apparently a standard for blu-ray).

So far I suppose:

MKV Pros
- can contain just about anything
- can probably use vanilla ffmpeg to move to .mkv container

MKV Cons
- I'd need to transcode audio to mp3 for my particular hardware use case (so, slower conversion)

TS Pros
- more error resiliance
- no audio transcode required
- can probably use vanilla ffmpeg to move to .ts container

TS Cons
- none apparent

Clarifications welcome.