[Libav-user] Timing Issues Only With Windows Media Player

Stephen H. Gerstacker stephen at napkinstudio.com
Fri Mar 14 19:16:48 CET 2014

That’s more to the question. Is there a “proper” way to create an MP4 / H.264 / AAC file?

I wrote some code to inject empty audio frames at the very beginning of the audio stream, which seems to help, but I had to restructure a lot of code to get it there. Am I missing a flag of the stream? the container?

Oddly enough, once the audio stream is initially padded, it’s fine. So I can have:

- 20 seconds of video
- 5 second audio pause, 5 second audio, 5 second pause, 5 second audio

The second audio part plays at the proper time, so it just seems like the initial audio padding is just needed.

I have similar code on the Mac side using AVFoundation and their encoder seems to push in empty audio packets.
- Stephen

On Mar 14, 2014, at 11:49 AM, wm4 <nfxjfg at googlemail.com> wrote:

> On Fri, 14 Mar 2014 09:34:31 -0400
> "Stephen H. Gerstacker" <stephen at napkinstudio.com> wrote:
>> I’m constructing a video file from pre-encoded packets. Video is H.264, Audio is AAC, and the container is MP4.
>> As an example, I have:
>> - 20 seconds of video
>> - 10 seconds of audio, starting at 5 seconds in.
>> I’m checking PTSs and writing with av_write_frame in the proper order. The resulting file works great in VLC and QuickTime, but if I open the video in Windows Media Player, that audio starts playing immediately. Everything else about the audio is fine, it just starts at the wrong time.
>> Any idea on why this would be happening? Is there a proper way to push audio in to a video file that doesn’t start immediately?
>> I’ve also tried av_interleaved_write_frame, but that didn’t change anything.
> For starters, does windows media player even allow audio to start at a
> different time? If so, you could e.g. take a "working" file and compare
> it with a ffmpeg produced file.
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