ffmpeg merge multiple (N) mono audio channels of a MXF video to multiple (M) stereo channels of MP4 video

Question

I have an MXF file with 16 audio mono streams and I need to recode it in a mp4 file with 2<=n<=16 channels merging input streams, e.g. input channels 1 and 2 on output channel 1 and 9 and 10 on output channel 2. This job will be done with ffmpeg. I read the documentation and found the amerge and amix filters that would be nice, but they output one channel only. Is there any solution for this problem?

Thanks, Laura

Find below the output of ffprobe on mxf file:

{ "streams":[ { "index":0, "codec_name":"mpeg2video", "codec_long_name":"MPEG-2 video", "profile":"4:2:2", "codec_type":"video", "codec_time_base":"1/25", "codec_tag_string":"[0][0][0][0]", "codec_tag":"0x0000", "width":1920, "height":1080, "coded_width":0, "coded_height":0, "has_b_frames":1, "sample_aspect_ratio":"1:1", "display_aspect_ratio":"16:9", "pix_fmt":"yuv422p", "level":2, "color_range":"tv", "color_space":"bt709", "color_transfer":"bt709", "color_primaries":"bt709", "chroma_location":"topleft", "field_order":"tt", "refs":1, "r_frame_rate":"25/1", "avg_frame_rate":"25/1", "time_base":"1/25", "start_pts":0, "start_time":"0.000000", "duration_ts":448, "duration":"17.920000", "bit_rate":"50000000", "disposition":{ "default":0, "dub":0, "original":0, "comment":0, "lyrics":0, "karaoke":0, "forced":0, "hearing_impaired":0, "visual_impaired":0, "clean_effects":0, "attached_pic":0, "timed_thumbnails":0 }, "tags":{ "file_package_umid":"0x060A2B340101010501010D2313000000968F75C6B5B34D649967EEDD0076B989" } }, { "index":1, "codec_name":"pcm_s24le", "codec_long_name":"PCM signed 24-bit little-endian", "codec_type":"audio", "codec_time_base":"1/48000", "codec_tag_string":"[0][0][0][0]", "codec_tag":"0x0000", "sample_fmt":"s32", "sample_rate":"48000", "channels":1, "bits_per_sample":24, "r_frame_rate":"0/0", "avg_frame_rate":"0/0", "time_base":"1/48000", "start_pts":0, "start_time":"0.000000", "duration_ts":860160, "duration":"17.920000", "bit_rate":"1152000", "bits_per_raw_sample":"24", "disposition":{ "default":0, "dub":0, "original":0, "comment":0, "lyrics":0, "karaoke":0, "forced":0, "hearing_impaired":0, "visual_impaired":0, "clean_effects":0, "attached_pic":0, "timed_thumbnails":0 }, "tags":{ "file_package_umid":"0x060A2B340101010501010D2313000000968F75C6B5B34D649967EEDD0076B989" } }, { "index":2, "codec_name":"pcm_s24le", "codec_long_name":"PCM signed 24-bit little-endian", "codec_type":"audio", "codec_time_base":"1/48000", "codec_tag_string":"[0][0][0][0]", "codec_tag":"0x0000", "sample_fmt":"s32", "sample_rate":"48000", "channels":1, "bits_per_sample":24, "r_frame_rate":"0/0", "avg_frame_rate":"0/0", "time_base":"1/48000", "start_pts":0, "start_time":"0.000000", "duration_ts":860160, "duration":"17.920000", "bit_rate":"1152000", "bits_per_raw_sample":"24", "disposition":{ "default":0, "dub":0, "original":0, "comment":0, "lyrics":0, "karaoke":0, "forced":0, "hearing_impaired":0, "visual_impaired":0, "clean_effects":0, "attached_pic":0, "timed_thumbnails":0 }, "tags":{ "file_package_umid":"0x060A2B340101010501010D2313000000968F75C6B5B34D649967EEDD0076B989" } }, { "index":3, "codec_name":"pcm_s24le", "codec_long_name":"PCM signed 24-bit little-endian", "codec_type":"audio", "codec_time_base":"1/48000", "codec_tag_string":"[0][0][0][0]", "codec_tag":"0x0000", "sample_fmt":"s32", "sample_rate":"48000", "channels":1, "bits_per_sample":24, "r_frame_rate":"0/0", "avg_frame_rate":"0/0", "time_base":"1/48000", "start_pts":0, "start_time":"0.000000", "duration_ts":860160, "duration":"17.920000", "bit_rate":"1152000", "bits_per_raw_sample":"24", "disposition":{ "default":0, "dub":0, "original":0, "comment":0, "lyrics":0, "karaoke":0, "forced":0, "hearing_impaired":0, "visual_impaired":0, "clean_effects":0, "attached_pic":0, "timed_thumbnails":0 }, "tags":{ "file_package_umid":"0x060A2B340101010501010D2313000000968F75C6B5B34D649967EEDD0076B989" } }, { "index":4, "codec_name":"pcm_s24le", "codec_long_name":"PCM signed 24-bit little-endian", "codec_type":"audio", "codec_time_base":"1/48000", "codec_tag_string":"[0][0][0][0]", "codec_tag":"0x0000", "sample_fmt":"s32", "sample_rate":"48000", "channels":1, "bits_per_sample":24, "r_frame_rate":"0/0", "avg_frame_rate":"0/0", "time_base":"1/48000", "start_pts":0, "start_time":"0.000000", "duration_ts":860160, "duration":"17.920000", "bit_rate":"1152000", "bits_per_raw_sample":"24", "disposition":{ "default":0, "dub":0, "original":0, "comment":0, "lyrics":0, "karaoke":0, "forced":0, "hearing_impaired":0, "visual_impaired":0, "clean_effects":0, "attached_pic":0, "timed_thumbnails":0 }, "tags":{ "file_package_umid":"0x060A2B340101010501010D2313000000968F75C6B5B34D649967EEDD0076B989" } }, { "index":5, "codec_name":"pcm_s24le", "codec_long_name":"PCM signed 24-bit little-endian", "codec_type":"audio", "codec_time_base":"1/48000", "codec_tag_string":"[0][0][0][0]", "codec_tag":"0x0000", "sample_fmt":"s32", "sample_rate":"48000", "channels":1, "bits_per_sample":24, "r_frame_rate":"0/0", "avg_frame_rate":"0/0", "time_base":"1/48000", "start_pts":0, "start_time":"0.000000", "duration_ts":860160, "duration":"17.920000", "bit_rate":"1152000", "bits_per_raw_sample":"24", "disposition":{ "default":0, "dub":0, "original":0, "comment":0, "lyrics":0, "karaoke":0, "forced":0, "hearing_impaired":0, "visual_impaired":0, "clean_effects":0, "attached_pic":0, "timed_thumbnails":0 }, "tags":{ "file_package_umid":"0x060A2B340101010501010D2313000000968F75C6B5B34D649967EEDD0076B989" } }, { "index":6, "codec_name":"pcm_s24le", "codec_long_name":"PCM signed 24-bit little-endian", "codec_type":"audio", "codec_time_base":"1/48000", "codec_tag_string":"[0][0][0][0]", "codec_tag":"0x0000", "sample_fmt":"s32", "sample_rate":"48000", "channels":1, "bits_per_sample":24, "r_frame_rate":"0/0", "avg_frame_rate":"0/0", "time_base":"1/48000", "start_pts":0, "start_time":"0.000000", "duration_ts":860160, "duration":"17.920000", "bit_rate":"1152000", "bits_per_raw_sample":"24", "disposition":{ "default":0, "dub":0, "original":0, "comment":0, "lyrics":0, "karaoke":0, "forced":0, "hearing_impaired":0, "visual_impaired":0, "clean_effects":0, "attached_pic":0, "timed_thumbnails":0 }, "tags":{ "file_package_umid":"0x060A2B340101010501010D2313000000968F75C6B5B34D649967EEDD0076B989" } }, { "index":7, "codec_name":"pcm_s24le", "codec_long_name":"PCM signed 24-bit little-endian", "codec_type":"audio", "codec_time_base":"1/48000", "codec_tag_string":"[0][0][0][0]", "codec_tag":"0x0000", "sample_fmt":"s32", "sample_rate":"48000", "channels":1, "bits_per_sample":24, "r_frame_rate":"0/0", "avg_frame_rate":"0/0", "time_base":"1/48000", "start_pts":0, "start_time":"0.000000", "duration_ts":860160, "duration":"17.920000", "bit_rate":"1152000", "bits_per_raw_sample":"24", "disposition":{ "default":0, "dub":0, "original":0, "comment":0, "lyrics":0, "karaoke":0, "forced":0, "hearing_impaired":0, "visual_impaired":0, "clean_effects":0, "attached_pic":0, "timed_thumbnails":0 }, "tags":{ "file_package_umid":"0x060A2B340101010501010D2313000000968F75C6B5B34D649967EEDD0076B989" } }, { "index":8, "codec_name":"pcm_s24le", "codec_long_name":"PCM signed 24-bit little-endian", "codec_type":"audio", "codec_time_base":"1/48000", "codec_tag_string":"[0][0][0][0]", "codec_tag":"0x0000", "sample_fmt":"s32", "sample_rate":"48000", "channels":1, "bits_per_sample":24, "r_frame_rate":"0/0", "avg_frame_rate":"0/0", "time_base":"1/48000", "start_pts":0, "start_time":"0.000000", "duration_ts":860160, "duration":"17.920000", "bit_rate":"1152000", "bits_per_raw_sample":"24", "disposition":{ "default":0, "dub":0, "original":0, "comment":0, "lyrics":0, "karaoke":0, "forced":0, "hearing_impaired":0, "visual_impaired":0, "clean_effects":0, "attached_pic":0, "timed_thumbnails":0 }, "tags":{ "file_package_umid":"0x060A2B340101010501010D2313000000968F75C6B5B34D649967EEDD0076B989" } } ], "format":{ "filename":"/media-caches/video-essence/VIDEO/MXF-XDCAM_HD422@50Mbps1080i25_16Ch/941.mxf", "nb_streams":9, "nb_programs":0, "format_name":"mxf", "format_long_name":"MXF (Material eXchange Format)", "start_time":"0.000000", "duration":"17.920000", "size":"135028296", "bit_rate":"60280489", "probe_score":100, "tags":{ "uid":"0a9ef41a-36b4-4066-a8a3-b95f62299b6c", "generation_uid":"e134647e-fea1-4673-91c1-afa277d13c00", "company_name":"Sony", "product_name":"MPC", "product_version":"v1.0", "application_platform":"Sony MXF Development Kit (Win32)", "product_uid":"060e2b34-0401-0103-0e06-0120027f0200", "modification_date":"2012-09-17T11:56:20.000000Z", "material_package_umid":"0x060A2B340101010501010D231300000081C32F48A63347D4890F55D3ADC25B99", "timecode":"00:35:30:08" } } }

Answer 1

The code is organised with line breaks. A \ breaks a line in a Unix shell.

ffmpeg -i "in.mxf" \
-filter_complex "\
[a:0][a:1]amerge=inputs=2[ch1ch2];\
[a:8][a:9]amerge=inputs=2[ch9ch10]" \
-map 'v:0' \
-map '[ch1ch2]' \
-map '[ch9ch10]' \
-c:v copy \
-c:a aac -b:a 128k -ar 48000 -ac 2 \
"out.mp4"

1. input
2. filter_complex (use " instead of '. If I use shell line breaks \ I get an error with single quotes ')
3. use amerge filter and select
   • 1st audio stream a:0 and
   • 2nd audio stream a:1,
   • merge them and
   • store it in output pad ch1ch2 (you can give it any name)
4. use another amerge filter and select
   • 9th audio stream a:8 and
   • 10th audio stream a:9,
   • merge them and
   • store it in output pad ch9ch10
5. map video stream (if you omit that, your output has no video)
6. map pad ch1ch2 to 1st audio stream
7. map pad ch9ch10 to 2nd audio stream
8. copy video stream (if you omit that, your video will be reencoded)
9. encode all audio streams with aac
10. output

Here the output has only the 2 mapped audio channels.

If you want to keep some of the remaining channels you have to map them. You can even add -map 0 right after Line 7 to stack all streams underneath your merged ones. (But of course you would end up with 2+16 audio streams.)

You can add more amerge filters. Separate them with ; You can also merge 3 audio streams with [a:0][a:1][a:2]amerge=inputs=3[ch1ch2ch3]. Name the audio channels with

-metadata:s:a:0 title="channel 1 and 2"

This is useful for testing because you can see the names in VLC.