Support for jo_mpeg files

[FrostKiwi]

There is a single header library doing simplistic MPEG-1 encoding called jo_MPEG. I converted it to C and wrote a blog post about it: https://blog.frost.kiwi/jo-mpeg-in-c/ and the original creator Jon Olick and his blog post is here: https://www.jonolick.com/home/mpeg-video-writer
The output plays back in VLC, MPV and Windows Media Player Legacy, but not with jsmpeg. Sample attached. (Zipped, as github does not permit .mpeg) sample.zip

jsmpeg reports JSMpeg: Possible garbage data. Skipping.

What is the reason? Is it the lack of container format or does the output stray too far from the MPEG-1 spec?

[phoboslab]

This encodes raw MPEG1 video, not the MPEG-TS container. You should be able to decode it by feeding it directly to JSMpeg.Decoder.MPEG1Video.

[FrostKiwi]

@phoboslab
Thanks! Nice, now the article has a live preview <3 https://blog.frost.kiwi/jo-mpeg-in-c/

To prevent custom code, I remuxed the sample.mpeg as output by jo_mpeg into MPEG-TS, as you mentioned via ffmpeg -c copy -r 30 -f mpegts -o sample.ts
sample_ts.zip

Couple things are weird:
mpv plays back the file properly, at 30fps and start immediately.
jsmpeg plays the file in localhost and is able to loop it after finishing the file. After uploading to GitHub and accesing via https://blog.frost.kiwi/jo-mpeg-in-c/ , jsmpeg plays the file, but once it finishes it locks-up and gets stuck somehow, not looping and not restart the video when pressing the window.

Also jsmpeg plays the file at Screen Refresh rate, 60hz in my case, instead of the stream's framerate of 30hz. Also on localhost, when repeating the file, the playback gets stuck for a second before beginning, whilst online, as previously mentioned, it gets stuck completely on the last frame.

I suspect this is due to timestamps being weird somehow. MPV cannot report the duration of the file or seek. Any suggestions on how to fix that?

[phoboslab]

Yeah, this is an issue with the timestamps. When trying to remux the sample.ts, ffmpeg gives this warning:

[mpegts @ 0x5576f302f080] Non-monotonous DTS in output stream 0:0; previous: 0, current: 0; changing to 1. This may result in incorrect timestamps in the output file.
[mpegts @ 0x5576f302f080] Timestamps are unset in a packet for stream 0. This is deprecated and will stop working in the future. Fix your code to set the timestamps properly

I guess we could detect invalid timestamps in the video/audio streams and ignore them (i.e. generate our own based on the framerate), but for now, instructing ffmpeg to generate proper presentation timestamps will work:

ffmpeg -fflags +genpts -i sample.ts -c copy sample-fixed.ts

[FrostKiwi]

instructing ffmpeg to generate proper presentation timestamps will work:

Fixed everything perfectly! Many thanks. Learned a ton in the process.