[FFmpeg-user] Audio Only Fragmented MP4

Discussion:

[FFmpeg-user] Audio Only Fragmented MP4 - SIDX

Ronak

2018-11-12 17:11:15 UTC

Hey All,

I noticed that ffmpeg always seems to generate a SIDX box when it's not really required for Audio Only content.

Example command:

ffmpeg -i atmosTest.mp4 -codec copy -hls_time 0.993 -hls_segment_type fmp4 -hls_flags single_file -hls_playlist_type vod atmosTestffmpeg.m3u8
ffmpeg version N-92272-g0e9c01f Copyright (c) 2000-2018 the FFmpeg developers
built with Apple LLVM version 10.0.0 (clang-1000.11.45.2)
configuration: --prefix=/Users/ronakp/ffmpeg_build --pkg-config-flags=--static --extra-cflags=-I/Users/ronakp/ffmpeg_build/include --extra-ldflags=-L/Users/ronakp/ffmpeg_build/lib --extra-libs=-lpthread --extra-libs=-lm --bindir=/Users/ronakp/bin --enable-libfdk_aac --enable-libmp3lame --enable-libopus --enable-nonfree
libavutil 56. 20.100 / 56. 20.100
libavcodec 58. 34.100 / 58. 34.100
libavformat 58. 19.102 / 58. 19.102
libavdevice 58. 4.106 / 58. 4.106
libavfilter 7. 38.100 / 7. 38.100
libswscale 5. 2.100 / 5. 2.100
libswresample 3. 2.100 / 3. 2.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'atmosTest.mp4':
Metadata:
major_brand : mp42
minor_version : 1
compatible_brands: mp42dby1isom
creation_time : 2018-09-07T19:17:49.000000Z
Duration: 00:02:40.80, start: 0.000000, bitrate: 769 kb/s
Stream #0:0(und): Audio: eac3 (ec-3 / 0x332D6365), 48000 Hz, 5.1(side), fltp, 768 kb/s (default)
Metadata:
creation_time : 2018-09-07T19:17:49.000000Z
handler_name : sound handler
Side data:
audio service type: main
[hls @ 0x7fbfc4825c00] Opening 'atmosTestffmpeg.m4s' for writing
[mp4 @ 0x7fbfc4827600] track 0: codec frame size is not set
Output #0, hls, to 'atmosTestffmpeg.m3u8':
Metadata:
major_brand : mp42
minor_version : 1
compatible_brands: mp42dby1isom
encoder : Lavf58.19.102
Stream #0:0(und): Audio: eac3 (ec-3 / 0x332D6365), 48000 Hz, 5.1(side), fltp, 768 kb/s (default)
Metadata:
creation_time : 2018-09-07T19:17:49.000000Z
handler_name : sound handler
Side data:
audio service type: main
Stream mapping:
Stream #0:0 -> #0:0 (copy)
Press [q] to stop, [?] for help
size=N/A time=00:02:40.76 bitrate=N/A speed= 397x
video:0kB audio:15075kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown

When you look at the generated .m4s file, you will see ftyp, moov, followed by a collection of sidx, moof and mdat atoms.

However, when I run a similar command using Apple's Tooling:

a45e60e46a79:Dolby ronakp$ mediafilesegmenter -a -r -s atmosTest.ec3
Nov 12 2018 11:58:52.713: ISO fragmented mode, forcing segments to start with I-Frame
Nov 12 2018 11:58:52.714: Processing file /Users/ronakp/Desktop/Dolby/atmosTest.ec3
Nov 12 2018 11:58:52.743: Wrote 0 to 578 to main.mp4
Nov 12 2018 11:58:52.748: Wrote 578 to 959266 to main.mp4
Nov 12 2018 11:58:52.749: segment bitrate 768.18 kbits/sec is new max
Nov 12 2018 11:58:52.756: Wrote 959266 to 1917954 to main.mp4
Nov 12 2018 11:58:52.763: Wrote 1917954 to 2876642 to main.mp4
Nov 12 2018 11:58:52.772: Wrote 2876642 to 3835330 to main.mp4
Nov 12 2018 11:58:52.777: Wrote 3835330 to 4794018 to main.mp4
Nov 12 2018 11:58:52.784: Wrote 4794018 to 5752706 to main.mp4
Nov 12 2018 11:58:52.793: Wrote 5752706 to 6711394 to main.mp4
Nov 12 2018 11:58:52.800: Wrote 6711394 to 7670082 to main.mp4
Nov 12 2018 11:58:52.880: Wrote 7670082 to 8628770 to main.mp4
Nov 12 2018 11:58:52.924: Wrote 8628770 to 9587458 to main.mp4
Nov 12 2018 11:58:52.966: Wrote 9587458 to 10546146 to main.mp4
Nov 12 2018 11:58:52.973: Wrote 10546146 to 11504834 to main.mp4
Nov 12 2018 11:58:53.017: Wrote 11504834 to 12463522 to main.mp4
Nov 12 2018 11:58:53.060: Wrote 12463522 to 13422210 to main.mp4
Nov 12 2018 11:58:53.102: Wrote 13422210 to 14380898 to main.mp4
Nov 12 2018 11:58:53.147: Wrote 14380898 to 15339586 to main.mp4
Nov 12 2018 11:58:53.147: Wrote 15339586 to 15441066 to main.mp4
Nov 12 2018 11:58:53.147: segment bitrate 768.24 kbits/sec is new max
Nov 12 2018 11:58:53.147: Unknown video dynamic range value 0
Nov 12 2018 11:58:53.147: average bit rate is 768.21 kbits/sec - max file bit rate is 768.24 kbits/sec

It generates a file without any SIDX atoms; only ftyp, moov & a collection of moof & mdat atoms.

Why does ffmpeg do this? How hard would it be to remove this behavior from ffmpeg?

Thanks,

Ronak

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Ronak

2018-11-15 23:46:41 UTC

Permalink

I'm taking a look at moving.c and the mov_write_sidx_tags calls; I'm assuming this is the area of the code that is responsible for this.

However, I'd have to have a way to detect the input streams are audio only; no video tracks. What would be the best way to do that?

Post by Ronak
Hey All,
I noticed that ffmpeg always seems to generate a SIDX box when it's not really required for Audio Only content.
ffmpeg -i atmosTest.mp4 -codec copy -hls_time 0.993 -hls_segment_type fmp4 -hls_flags single_file -hls_playlist_type vod atmosTestffmpeg.m3u8
ffmpeg version N-92272-g0e9c01f Copyright (c) 2000-2018 the FFmpeg developers
built with Apple LLVM version 10.0.0 (clang-1000.11.45.2)
configuration: --prefix=/Users/ronakp/ffmpeg_build --pkg-config-flags=--static --extra-cflags=-I/Users/ronakp/ffmpeg_build/include --extra-ldflags=-L/Users/ronakp/ffmpeg_build/lib --extra-libs=-lpthread --extra-libs=-lm --bindir=/Users/ronakp/bin --enable-libfdk_aac --enable-libmp3lame --enable-libopus --enable-nonfree
libavutil 56. 20.100 / 56. 20.100
libavcodec 58. 34.100 / 58. 34.100
libavformat 58. 19.102 / 58. 19.102
libavdevice 58. 4.106 / 58. 4.106
libavfilter 7. 38.100 / 7. 38.100
libswscale 5. 2.100 / 5. 2.100
libswresample 3. 2.100 / 3. 2.100
major_brand : mp42
minor_version : 1
compatible_brands: mp42dby1isom
creation_time : 2018-09-07T19:17:49.000000Z
Duration: 00:02:40.80, start: 0.000000, bitrate: 769 kb/s
Stream #0:0(und): Audio: eac3 (ec-3 / 0x332D6365), 48000 Hz, 5.1(side), fltp, 768 kb/s (default)
creation_time : 2018-09-07T19:17:49.000000Z
handler_name : sound handler
audio service type: main
major_brand : mp42
minor_version : 1
compatible_brands: mp42dby1isom
encoder : Lavf58.19.102
Stream #0:0(und): Audio: eac3 (ec-3 / 0x332D6365), 48000 Hz, 5.1(side), fltp, 768 kb/s (default)
creation_time : 2018-09-07T19:17:49.000000Z
handler_name : sound handler
audio service type: main
Stream #0:0 -> #0:0 (copy)
Press [q] to stop, [?] for help
size=N/A time=00:02:40.76 bitrate=N/A speed= 397x
video:0kB audio:15075kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
When you look at the generated .m4s file, you will see ftyp, moov, followed by a collection of sidx, moof and mdat atoms.
a45e60e46a79:Dolby ronakp$ mediafilesegmenter -a -r -s atmosTest.ec3
Nov 12 2018 11:58:52.713: ISO fragmented mode, forcing segments to start with I-Frame
Nov 12 2018 11:58:52.714: Processing file /Users/ronakp/Desktop/Dolby/atmosTest.ec3
Nov 12 2018 11:58:52.743: Wrote 0 to 578 to main.mp4
Nov 12 2018 11:58:52.748: Wrote 578 to 959266 to main.mp4
Nov 12 2018 11:58:52.749: segment bitrate 768.18 kbits/sec is new max
Nov 12 2018 11:58:52.756: Wrote 959266 to 1917954 to main.mp4
Nov 12 2018 11:58:52.763: Wrote 1917954 to 2876642 to main.mp4
Nov 12 2018 11:58:52.772: Wrote 2876642 to 3835330 to main.mp4
Nov 12 2018 11:58:52.777: Wrote 3835330 to 4794018 to main.mp4
Nov 12 2018 11:58:52.784: Wrote 4794018 to 5752706 to main.mp4
Nov 12 2018 11:58:52.793: Wrote 5752706 to 6711394 to main.mp4
Nov 12 2018 11:58:52.800: Wrote 6711394 to 7670082 to main.mp4
Nov 12 2018 11:58:52.880: Wrote 7670082 to 8628770 to main.mp4
Nov 12 2018 11:58:52.924: Wrote 8628770 to 9587458 to main.mp4
Nov 12 2018 11:58:52.966: Wrote 9587458 to 10546146 to main.mp4
Nov 12 2018 11:58:52.973: Wrote 10546146 to 11504834 to main.mp4
Nov 12 2018 11:58:53.017: Wrote 11504834 to 12463522 to main.mp4
Nov 12 2018 11:58:53.060: Wrote 12463522 to 13422210 to main.mp4
Nov 12 2018 11:58:53.102: Wrote 13422210 to 14380898 to main.mp4
Nov 12 2018 11:58:53.147: Wrote 14380898 to 15339586 to main.mp4
Nov 12 2018 11:58:53.147: Wrote 15339586 to 15441066 to main.mp4
Nov 12 2018 11:58:53.147: segment bitrate 768.24 kbits/sec is new max
Nov 12 2018 11:58:53.147: Unknown video dynamic range value 0
Nov 12 2018 11:58:53.147: average bit rate is 768.21 kbits/sec - max file bit rate is 768.24 kbits/sec
It generates a file without any SIDX atoms; only ftyp, moov & a collection of moof & mdat atoms.
Why does ffmpeg do this? How hard would it be to remove this behavior from ffmpeg?
Thanks,
Ronak

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Carl Eugen Hoyos

2018-11-16 22:16:46 UTC

Permalink

Post by Ronak
I'm taking a look at moving.c and the mov_write_sidx_tags calls; I'm
assuming this is the area of the code that is responsible for this.
However, I'd have to have a way to detect the input streams are audio only;
no video tracks. What would be the best way to do that?

I suspect the number of input streams is irrelevant, you are probably
interested in the output streams within the mov file, you can look at
mov->nb_streams or possibly mov->tracks (there may be easier ways
though).

Please avoid top-posting here, Carl Eugen
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ffm

Ronak

2018-11-30 23:58:11 UTC

Permalink

Hey Carl,

I figured out the correct fix for this, based on your suggestion.

I'm going to send a patch for this to the dev mailing list. Appreciate your help to review my change.

Ronak

Post by Carl Eugen Hoyos

I suspect the number of input streams is irrelevant, you are probably
interested in the output streams within the mov file, you can look at
mov->nb_streams or possibly mov->tracks (there may be easier ways
though).
Please avoid top-posting here, Carl Eugen
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