Embedded mp4 subtitles support (dvd_subtitles)?

[jakubvojacek]

System info

Operating System: latest debian
Shaka Packager Version: packager version daac686-release

Issue and steps to reproduce the problem

I have read on shaka's repository homepage that

WebVTT in both text form and embedded in MP4

I have managed to package vtt subtitles quite easily however I was wondering how do subtitles embedded in mp4 work. I have MKV file that has dvd_subtitles Stream #0:4(cze): Subtitle: dvd_subtitle, 720x576. I tried to get them into mp4 via ffmpeg -txt_format bitmap -i frozen.mkv -map 0:4 -c copy subs.mp4 or ffmpeg -i frozen.mkv -map 0:4 -c copy subs.mp4 into an mp4 file (not sure which is correct, but neither works).

Packager Command:

packager  'in=frozen.mkv_288.mp4,stream=video,init_segment=frozen.mkv_video_288.mp4,segment_template=video_288_frozen.mkv-$Number$.mp4'  'in=subs.mp4,stream=text,init_segment=srt_init.mp4,segment_template=srt_$Number$.mp4,language=cs' --mpd_output frozen.mkv.mpd --generate_static_mpd

I would expect that this would create playbable MPD manifest. However it ends with Segmentation fault instead.

Can you please guide what part I am doing wrong (could be ffmpeg, could be packager?) and whether is this even possible to achieve?

Thank you

[vaage]

@jakubvojacek Yes, we support both reading and writing webvtt subtitles from text and mp4. Could you clarify one thing for me, which are you trying to do:

• VTT in Text --> VTT in MP4
• VTT in MP4 --> VTT in MP4
• VTT in MP4 --> VTT in Text

The only scenario that is not currently supported right now is VTT in MP4 --> VTT in Text. So as long as you are not intending to do that, it should work.

Can you supply us with the input files that you are feeding to the packager so that we can reproduce this locally?

[jakubvojacek]

After reading your post, I guess that what I want is not possible. The subtitles are not encoded in vtt but as dvd subtitles, therefore images I believe.

I have attached the sample mkv frozen.mkv.zip file from which I tried to get subtitles out using the ffmpeg command shared in my first post. Anyway, I am also attaching the mp4 subtitles that I have generated subs.mp4.zip

In order for you to check why the seg fault is thrown instead of some regular error, I am also attaching all files required for the packager command from my first post frozen.zip

Thank you
Jakub

[vaage]

Thank you @jakubvojacek. I am going to label this as a bug to investigate why we are getting a segfault.

[vaage]

We had a partial solution for inputting MP4s, but it was not complete and would yield incorrect results. In this part of the pipeline, there was the previously mentioned segfault.

We have removed that part of the pipeline, so the seg-faulting-code is now gone, which in a way fixes the issue, so I will be closing this issue.

Right now we do not have immediate plans to add back the mp4 input code, as there has not been enough demand for it. When there is enough demand voiced from the community, we are open to scheduling the work (#405).