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kirubakaran

I need to encode mp4s using these flags, so that firefox will render it correctly

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They may have tried to open arbitrary mp4s and had Firefox not render it.Firefox seems to only render MP4 files that use yuv colorspace and aa3 audio channels, which require specific ffmpeg flags during transcoding. It took me a day of grinding whackamole to find the magic set of arguments to make all recent, popular browsers actually display a video:https://github.com/photostructure/photostructure-for-servers...
Possibly a useful doc for ya then: https://developer.mozilla.org/en-US/docs/Web/Media/Formats/V... . And beyond that it depends on the OS, so windows/linux/mac/ios/android/etc will all vary.Some of this is also probably due to using ffmpeg directly, tbh. It's very happy to produce irrational combinations of things that are technically allowed by specs but not implemented anywhere in practice, often exacerbated by it trying to preserve metadata / colorspace / etc where technically possible.