Frame rate change when copying video streams with FFmpeg.

[naoto89]

I have a question regarding framerate changes when copying H.264 video streams from MKV container to MP4.

I know the process to do it. I've used FFmpeg and MP4box (sometimes using YAMB GUI and other times just CLI). Copying video streams with FFmpeg is very convenient when the source videos have VFR and FFmpeg has no problem reading it, while with MP4Box things happen irregular situations that vary in each version but in general MP4Box works better only when input and output videos are CFR and most of the time it is not necessary to specify the FPS number because in recent versions of MP4Box it automatically detects the speed and number of frames from input videos. However, when copying CFR videos with FFmpeg, all input videos are treated as it were VFR videos and that's why when checking with MediaInfo it says that the output videos were changed to VFR and shows the different numbers of original frame rate, number of minimum frame rate and number of maximum frame rate. Is there a way to make FFmepg better differentiate and detect when input videos are CFR or VFR to prevent changes for output video streams that were copied?

The FFmpeg command line that I generally use is more or less like this.

FOR %%I in (%inputdir%\*.MKV) DO "%ffmpeg%" -i "%%I" -codec copy "%outputdir%\%%~nI.mp4"

I know that everything can be solved with -r [fps] but that would mean having to modify the command line every time I want to do batch conversion for several files and I want to avoid that, that's why I already have .bat files made with variables to keep things simple.

[davexnet]

See this thread:
https://forum.videohelp.com/threads/405114-ffmpeg-MKV-to-MP4-without-rencode-makes-out...-rate-variable

[naoto89]

After having read all that thread and doing other tests with more current FFmpeg and MP4Box bin, I came to the conclusion that currently the only way to get a video that keeps the same framerate when copying the video streams, first is to demux the H.264 video and then mux the raw videos to the new container. I don't like that because it means having more temporary files (which means having more storage space). With MP4Box I can understand that it is necessary to have raw H264 video because MP4Box doesn't have support to open MKV container and copy video streams. Luckily, MP4Box can now detect when a video is CFR and VFR, so there's almost no need to specify the fps number as before, because otherwise the new video would default to 25 fps. Even so, FFmpeg should get better at copying video streams.

[rbouqueau]

GPAC/MP4Box maintainer here. In general if you see any weird content we're always happy to help at https://github.com/gpac/gpac/issues

> MP4Box doesn't have support to open MKV container

It does since GPAC 0.9 (circa 2019).

> it is necessary to have raw H264 video

By going back to raw without duming the original timestamps, you take the risk of a sligh desync. MP4Box allows to reparse for you:

-add src.mkv --reparse

.

[naoto89]

> MP4Box doesn't have support to open MKV container

It does since GPAC 0.9 (circa 2019).

Since 2019? Wow, I didn't know that and the strangest thing is in GUI tools like MeGUI that use MP4Box as MP4 Muxer, MKV is never mentioned as a supported file for video input and FLAC is also not mentioned among supported audio files. In fact, I also didn't know that the MP4 container could already support FLAC audio from a few years ago and until recently I found out because I read it in a question made to FFmpeg support, so I even tested with MP4Box and my surprise was that it supported FLAC audios but it never occurred to me to test with an input MKV file.

> it is necessary to have raw H264 video

By going back to raw without duming the original timestamps, you take the risk of a sligh desync. MP4Box allows to reparse for you:

-add src.mkv --reparse

.

The parameter --reparse does not appear in the help info even if I run mp4box.exe -h all. Even in the latest versions of MP4Box, the way that the help info is displayed has changed a lot and in some cases (as -h format) it says to consult it using gpac.exe but the problem is that I only use MP4Box standalone (in fact, I am using a compiled version with Media AutoBuild Suite and other times I copy MP4Box.exe that is included in MeGUI)

[rbouqueau]

Thanks for the feedback. We made a lot of work to make GPAC more useful, safer, cleaner, and better documented. The Website should update soon. However it's hard to deal with such a level of complexity and keep everyone up to date. Let me know if you have suggestions (could be to post on this forum at each feature/release, etc.).

I'm also wondering if providing a GUI could make it easier for people to interact with the tool. There could be a WebAssembly playground from the Website or a "help center" able to centralize ressources. Ideas welcome

> The parameter --reparse does not appear in the help

The discoverability of the options is a real concern. The 'reparse' option doesn't belong to the MP4Box application, it belongs to a third-party module which MP4Box may leverage. For now you can type

MP4Box -h reparse

to know more.

[naoto89]

Thanks for the feedback. We made a lot of work to make GPAC more useful, safer, cleaner, and better documented. The Website should update soon. However it's hard to deal with such a level of complexity and keep everyone up to date. Let me know if you have suggestions (could be to post on this forum at each feature/release, etc.)

Although it is important to update documentation on website, don't neglect the info that is displayed when run mp4box.exe -h. As I mentioned, that has changed so much in the last years and versions that I feel like some info has been lost that is now only displayed with gpac.exe. I remember that before when I ran mp4box.exe -h all I could find a list of compatible formats but now that list no longer appears and that's why I'm not surprised that I didn't find out about things like the current support with MKV or FLAC.

In fact, there is a problem with MP4Box that goes back years and has not been fixed until now. It has to do with the tags of the streams. The problem comes more or less since MP4Box 0.6.0, when "name=" is not set as title for each stream, somehow MP4Box adds a title but the content is none other than a copied part of the command line used or the GPAC version number. The only way to avoid that is by adding "name=" but leaving the field blank and as the last (or single) of all parameters set for tracks after set others like language.

I'm also wondering if providing a GUI could make it easier for people to interact with the tool. There could be a WebAssembly playground from the Website or a "help center" able to centralize ressources. Ideas welcome

A GUI that is aware of MP4Box updates has always been needed. YAMB has always struck me as one of the best GUIs using MP4Box but, besides not being updated for many years, I was limited to using a single file per session and usually I work with multiple files and do batch conversion. My MP4Box GUI on the other hand, had other limitations such as not being able to work correctly with VFR videos. MeGUI's MP4 Muxer also has the same limitations despite using the most recent MP4Box bin in every MeGUI release.

The discoverability of the options is a real concern. The 'reparse' option doesn't belong to the MP4Box application, it belongs to a third-party module which MP4Box may leverage. For now you can type

MP4Box -h reparse

to know more.

Sorry, but MP4Box gives an error with a red text that says

Option -reparse unknown, please check usage.

[rbouqueau]

Noted, we'll think about this.

Note that you can get the format list this way:

$ MP4Box -h format
see [filters documentation](Filters), `gpac -h codecs`, `gpac -h formats` and `gpac -h protocols`

About reimporting the content, the wiki contains some examples using ':unframer', which seems to be the more generic way to force parsing the content again: https://github.com/gpac/gpac/wiki/filters-oneliners#remultiplexing

[naoto89]

Well, now I understand why MeGUI can't take advantage of the capabilities that MP4Box currently has, MeGUI only uses the standalone MP4Box, not the full GPAC package which is only available by downloading installers. MP4Box is dependent on external filters to work (for import MKV it's like this) instead of having everything built in static binary. Even if I were to build MP4Box again with MABS, it would still have the same static bin that is missing features that are only in GPAC packages. It's a shame.

[rbouqueau]

Nope, you can make a static build that embeds the modules That's what MABS seems to do btw: https://github.com/m-ab-s/media-autobuild_suite/blob/master/build/media-suite_compile.sh#L1486. Let us know if you see any issue.

[naoto89]

Nope, you can make a static build that embeds the modules That's what MABS seems to do btw: https://github.com/m-ab-s/media-autobuild_suite/blob/master/build/media-suite_compile.sh#L1486. Let us know if you see any issue.

Well, It has taken me a while to do it because errors that always happen when run MABS but I could build a new static MP4Box. However, I still get the same error.

[core] Creating default credential key in I:\MP4Box/creds.key, use -cred=PATH/TO_FILE to overwrite
Filter fin failed to setup: Filter not found for the desired type
[Importer] Error probing \CS\input\input.mkv
Failure while importing import: Filter not found for the desired type
Error importing \CS\input\input.mkv#1: Filter not found for the desired type

I have other question. What is that creds.key file that is created in the MP4Box.exe directory? In previous versions that never happened.

[rex144]

I have other question. What is that creds.key file that is created in the MP4Box.exe directory? In previous versions that never happened.

I am curious about this as well.

[rbouqueau]

$ MP4Box -h cred
-cred (string):                path to 128 bits key for credential storage

We (I am a GPAC maintainer) added this for people storing content e.g. on remote protected storage such as AWS S3.

Since GPAC 0.9 (in 2020) we have a new architecture that allows MP4Box to be more flexible. So it can also process remote or live sources. Happy to answer your questions if you have some

We are also preparing some news, I should come and post here more often!

[naoto89]

Since GPAC 0.9 (in 2020) we have a new architecture that allows MP4Box to be more flexible. So it can also process remote or live sources.

Download live streams using MP4Box/GPAC? This is new for me. So do you think a stream can be downloaded from vustreams.com for example??

[rbouqueau]

Yes. In addition we introduced a new tool called "gpac". To download a content just do "gpac -i INPUT -o OUTPUT". For example "gpac -i http://..../xxx.mpd -o dump.mp4".

You can also dump all the qualities or transcode on-the-fly. You can find some command-lines here.

Let me know if you have questions or ideas. I think we've made a lot of things (and we are now the main packager of Netflix) but we did not necessarily advertised it on the right channels. Any advice welcome

We also made a survey. Despite what's written it is not too late to fill it!