Transcode HLS m3u8 to MP4 and include text track

Question

Is it possible with FFMPEG to convert a m3u8 to a MP4 and keep the captions (text) track?

When looking at the Apple stream, https://devimages.apple.com.edgekey.net/streaming/examples/bipbop_4x3/bipbop_4x3_variant.m3u8 I see that the video stream makes mention of Closed Captions, but I can't seem to find a way to extract them.

Stream #0:0: Video: h264 (Main) ([27][0][0][0] / 0x001B), yuv420p(tv, smpte1
70m/smpte170m/bt709), 400x300, Closed Captions, 29.92 fps, 29.92 tbr, 90k tbn, 1
80k tbc

The multiple attempts I have made transcode to mp4 but it drops the captions.

I have used VLC on the manifest and it has "subtitles" but after transcode the mp4 doesn't.

Used the command: ffmpeg -i https://devimages.apple.com.edgekey.net/streaming/examples/bipbop_4x3/bipbop_4x3_variant.m3u8 -c copy -bsf:a aac_adtstoasc out.mp4

Answer 1

I did manage to pull together enough pieces on information to complete this. It is a combination of 3 commands.

Using ffmpeg version 2.8.4

First, the playlist segments need to be merged into a single MPEG-TS file:

ffmpeg -i [playlist_url].m3u8 -c copy [filename].ts

Next, we need to extract the Closed Captions from the file:

ffmpeg -f lavfi -i "movie=[filename_from_last_step].ts[out0+subcc]" [filename].srt

Note: I could only get it to work if the ts file and the cmd's current path matched.

Lastly, you merge the ts and srt file and transcode to MP4:

ffmpeg -i [filename_from_first_step].ts -i [captions].srt -c:v copy -bsf:a aac_adtstoasc -c:s mov_text [out_file_name].mp4

This will give you a MP4 with the captions embedded, as well as a stand-alone srt file if your player doesn't support embedded captions.

Answer 2

If Closed Captions means a CEA-608 or 708 stream, then those are weirdly packetized i.e. embedded within the video stream, and ffmpeg cannot copy or encode them.

You can try to use CCextractor to extract them. If it does not work on the stream. Download the individual segments, concat them and try with that.

Once extracted, you can encode them using -c:s mov_text into the MP4.