ffmpeg losing subtitle track converting MP4 to MP4

[the_steve_randolph]

I am researching a seemingly different conversion problem and I ran across this basic issue. The MP4 file has no chapters, a single title (that is, no multiple titles like some DVDs), a single audio track, a single video track, and, a single subtitle track. Just as a test to prove that nothing should change, I ran this command:

ffmpeg -i input.mp4 -c copy output.mp4

When I looked at the output file, the subtitle track is missing. Obviously, I don't want that to happen, but, I don't know why it happened. I have attached the console output from that command. Anybody know what is going on?

[the_steve_randolph]

I see from another thread that a user lost subtitles while converting from MK4 to MP4. One reply mentioned that MP4 does not support as many subtitle formats as MKV. I know that subtitles can be text-based or image-based, but, I don't know what other formats there might be. I am trying to learn and use ffmpeg for all of my conversions. According to the ffmpeg console output, the information related to the MP4 subtitle track is:

mov_text (tx3g / 0x67337874), 793,72, 0 kb/s (default)

[ProWo]

Use clever FFmpeg-GUI.
Load your mkv, main, multiplex, your streams are already loaded, select mp4 as container, set your target file, click on multiplex. done.
If your subtitle is srt, ass or ssa then it will be automatically converted to mov_text, the only subtitle accepted by the mp4 container.

[the_steve_randolph]

Use clever FFmpeg-GUI.
Load your mkv, main, multiplex, your streams are already loaded, select mp4 as container, set your target file, click on multiplex. done.
If your subtitle is srt, ass or ssa then it will be automatically converted to mov_text, the only subtitle accepted by the mp4 container.

Thanks for the suggestion, but, I am trying to find an answer to the ffmpeg command. And, I was simply asking why ffmpeg loses subtitles when doing a simple copy. Plus, you missed the part where I was converting MP4 to MP4, not from MKV to MP4.

[ProWo]

And, I was simply asking why ffmpeg loses subtitles when doing a simple copy. Plus, you missed the part where I was converting MP4 to MP4, not from MKV to MP4.

Try

ffmpeg -i input.mp4 -c:v copy -c:a copy -c:s mov_text output.mp4

[krykmoon]

another thing to try is explicitly tell FFMPEG to map all streams .. should be something like...

ffmpeg -i input.mp4 -map 0 -c copy output.mp4

[the_steve_randolph]

OK, both of these solutions worked:

ffmpeg -i input.mp4 -c:v copy -c:a copy -c mov_text output.mp4

ffmpeg -i input.mp4 -map 0 -c copy output.mp4


When I do my original statement, I look at the console output and towards the end, it has a label called "stream mapping" that is missing the subtitle stream. With those other two commands, under that label it has the subtitle stream listed like this:

Stream #0:2 -> #0:2 (copy)


I accept that these work and my original statement does not work. Now the question is: why?

Why is "-c copy" getting the video and audio streams but not the subtitle stream? Maybe ffmpeg's default stream handling doesn't have enough love/respect for the subtitle stream?


BTW, this statement also works:

ffmpeg -i input.mp4 -c:v copy -c:a copy -c copy output.mp4


As a side note, how can I put a command statement inside of a "Code:" box like y'all have done?

[krykmoon]

As a side note, how can I put a command statement inside of a "Code:" box like y'all have done?

You can manually enclose the code part into [CODx][/CODx] tags (where x = letter E) .. or use the # icon ("Wrap CODE text around selected text") from the formatting bar (not available when you quick reply)

[the_steve_randolph]

OK, I found this: [link](https://ffmpeg.org/ffmpeg.html#Automatic-stream-selection)

Under "4.1.1 Automatic stream selection" there is this statement:

"for subtitles, it is the first subtitle stream found but there’s a caveat. The output format’s default subtitle encoder can be either text-based or image-based, and only a subtitle stream of the same type will be chosen."

So, given my issue, this would seem to indicate that the default subtitle encoder for MP4 is NOT text-based since my MP4's subtitle track is "mov_text". That would explain why the "Stream #0:2 -> #0:2 (copy)" is not shown in the console output from my original statement but "Stream #0:2 -> #0:2 (copy)" is shown/included in the two solutions provided above.

Am I understanding/interpreting this correctly?

[the_steve_randolph]

You can manually enclose the code part into [CODx][/CODx] tags (where x = letter E) .. or use the # icon ("Wrap CODE text around selected text") from the formatting bar (not available when you quick reply)

ffmpeg -i input.mp4 -c:v copy -c:a copy -c copy output.mp4

Thanks!