[FFmpeg-user] How can I extract the last few seconds of a GoPro video losslessly with FFmpeg so that it keeps telemetry info and keeps the original stream order?

[Franck Dernoncourt]

I want to extract the last few seconds of a GoPro video losslessly with
FFmpeg so that it keeps telemetry info and keeps the original stream order.

A GoPro video has 4 streams, in that order:

   1. Stream #0:0[0x1](eng): Video
   2. Stream #0:1[0x2](eng): Audio
   3. Stream #0:2[0x3](eng): Data: none (tmcd / 0x64636D74) (default)
   4. Stream #0:3[0x4](eng): Data: bin_data (gpmd / 0x646D7067), 59 kb/s
   (default)

Details:

 Stream #0:0[0x1](eng): Video: hevc (Main) (hvc1 / 0x31637668),
yuvj420p(pc, bt709), 3840x2160 [SAR 1:1 DAR 16:9], 59703 kb/s, 59.94
fps, 59.94 tbr, 60k tbn (default)
      Metadata:
        creation_time   : 2024-11-23T23:10:03.000000Z
        handler_name    : GoPro H.265
        vendor_id       : [0][0][0][0]
        encoder         : GoPro H.265 encoder
        timecode        : 23:26:28:23
  Stream #0:1[0x2](eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000
Hz, stereo, fltp, 189 kb/s (default)
      Metadata:
        creation_time   : 2024-11-23T23:10:03.000000Z
        handler_name    : GoPro AAC
        vendor_id       : [0][0][0][0]
        timecode        : 23:26:28:23
  Stream #0:2[0x3](eng): Data: none (tmcd / 0x64636D74) (default)
      Metadata:
        creation_time   : 2024-11-23T23:10:03.000000Z
        handler_name    : GoPro TCD
        timecode        : 23:26:28:23
  Stream #0:3[0x4](eng): Data: bin_data (gpmd / 0x646D7067), 59 kb/s (default)
      Metadata:
        creation_time   : 2024-11-23T23:10:03.000000Z
        handler_name    : GoPro MET

I try to use this command to extract the last few seconds of a GoPro video
with ffmpeg so that it keeps telemetry info and keeps the original stream
order:

ffmpeg -sseof -10 -i input.MP4 -map 0:v -map 0:a -map 0:3 -c copy
-copy_unknown output.MP4

However, it inverses the order of Stream #0:2[0x3](eng) and Stream
#0:3[0x4](eng), i.e. the output file output.MP4 has 4 streams, in that
order:

   1. Stream #0:0[0x1](eng): Video
   2. Stream #0:1[0x2](eng): Audio
   3. Stream #0:3[0x3](eng): Data: bin_data (gpmd / 0x646D7067), 59 kb/s
   (default)
   4. Stream #0:2[0x4](eng): Data: none (tmcd / 0x64636D74) (default)

Stream details of the output file output.MP4:

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'output.MP4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2mp41
    encoder         : Lavf61.7.100
  Duration: 00:00:10.24, start: 0.000000, bitrate: 60393 kb/s
  Stream #0:0[0x1](eng): Video: hevc (Main) (hvc1 / 0x31637668),
yuvj420p(pc, bt709), 3840x2160 [SAR 1:1 DAR 16:9], 60132 kb/s, 59.94
fps, 59.94 tbr, 60k tbn (default)
      Metadata:
        handler_name    : GoPro H.265
        vendor_id       : [0][0][0][0]
        encoder         : GoPro H.265 encoder
        timecode        : 23:26:28:23
  Stream #0:1[0x2](eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000
Hz, stereo, fltp, 189 kb/s (default)
      Metadata:
        handler_name    : GoPro AAC
        vendor_id       : [0][0][0][0]
  Stream #0:2[0x3](eng): Data: bin_data (gpmd / 0x646D7067), 60 kb/s (default)
      Metadata:
        handler_name    : GoPro MET
  Stream #0:3[0x4](eng): Data: none (tmcd / 0x64636D74), 0 kb/s
      Metadata:
        handler_name    : GoPro H.265
        timecode        : 23:26:28:23

It is tempting to instead use the following command, since, as slhck
<https://superuser.com/users/48078/slhck> wrote
<https://superuser.com/a/539649/116475>, "the order of the -map options
determines the order of the streams in the output file":

ffmpeg -sseof -10 -i input.MP4 -map 0:v -map 0:a -map 0:2 -map 0:3 -c
copy output.MP4

However, one can't use -map on streams that FFmpeg doesn't understand, and
as a result, one gets this error:

[mp4 @ 00000292a73dd140] You requested a copy of the original timecode
track so timecode metadata are now ignored
[mp4 @ 00000292a73dd140] Could not find tag for codec none in stream
#2, codec not currently supported in container
[out#0/mp4 @ 00000292a793ec40] Could not write header (incorrect codec
parameters ?): Invalid argument
Conversion failed!

One may otherwise try to move -copy_unknown in front of -map 0:3, i.e.:

ffmpeg -sseof -10 -i input.MP4 -map 0:v -map 0:a -copy_unknown -map
0:3 -c copy  output.MP4

But FFmpeg doesn't care about the order of -copy_unknown relative to -map so
that doesn't change the stream order.

I'm out of ideas. For testing convenience, here is an example of a GoPro
video file
<https://ia803401.us.archive.org/19/items/images-for-questions/GoPro_file_example.MP4>
(18.5
MiB). Rename it as input.MP4 to try the aforementioned commands and use -sseof
-1 instead of -sseof -10 since the video is only 2-second long.

How can I extract the last few seconds of a GoPro video losslessly with
ffmpeg so that it keeps telemetry info *and keeps the original stream order*?
Thanks!