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I have a few videos I have to convert for a website. They are PowerPoint slides with a narration track over top. The originals I have to work with are in m4v format. I have converted them to mp4 and webm, but it seems like the video in the converted files plays too quickly. The audio doesn't match up. I used ffmpeg to convert to mp4 format. Is there an option I could pass in to keep the audio and video together?

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Please show your actual ffmpeg commands and the complete ffmpeg console outputs. What player(s) and browser(s) are you testing the output with? – LordNeckbeard Jan 20 '14 at 19:15

It sounds like the video frame rate probably got messed up. You need to make sure you compress the video to the same framerate in webm as the source is. Also, m4v and mp4 are synonyms, you don't need to alter the file, you can just change the extension.

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Hi AJ, simply changing the file extension worked for the m4v and mp4 conversion! Thanks! And I did notice that the images in the webm version were kind of ugly. Looks like my mp4 file has a bitrate of 241 kb/s, and the webm (I didn't specify any options in the command) came out at 79. How do I keep them the same? – eljefejb Jan 20 '14 at 21:21
@eljefejb Refer to the FFmpeg vpx (WebM) Encoding Guide. – LordNeckbeard Jan 21 '14 at 18:18

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