Background on Video Encoding

Closed Captioning with CaptionSync allows you to get encoded outputs using our Video Encoding feature. This article describes the several aspects related to this service.

For complete information on how to use our Video Encoding service see our Video Encoding tutorial.

1. For most applications, caption data resides in "side-car" files – that is, files separate from your video. The player picks up these caption files when the video is played and uses them to place the captions on the screen. CaptionSync is designed to return these side-car caption files to you, and for most applications these files will be all you need to display your captions. However, there are a few circumstances where you may want or need to encode the caption data back into your video:

• Convenience: If you want to send your video electronically and want it all in a single file, it may be more convenient to encode the captions into the video.
• Playback on iOS devices: iOS devices will support captions and subtitles, but they must be encoded into the video file; side-car files are not supported on these devices.
• Playback on players that do not support captioning: some players have no support for closed captions or subtitles; for such players, open captioning is the only option.
• Broadcast applications: many broadcasters require the caption data to be encoded into the video to very specific specifications in order that all of the equipment that will subsequently process the video data will know where to find the caption data.

2. Video Encoding is a service with an extra cost. You can see pricing in the Supplementary services price sheet pdf, on the Help page, in your account.

3. Not every media format (or player) supports a method of encoding the caption data into the media file, so the opportunity to encode the caption data and the method of doing so will vary with your media type.

4. The M4V, F4V, and MP4 extensions are essentially interchangeable. Video Encoding will typically name the resultant file as a .MP4.

5. It currently only applies to MP4, F4V, M4V, and MOV files. So if you submit a WMV or MP3, Video Encoding will not be applied and you will not be charged. List of URLs YouTube or Vimeo videos cannot have Video Encoding applied to them.

6. MOV input files should have MP4 video and audio codecs used.

7. Since these files can be rather large, the resultant file will only be stored for about 90 days from creation date – so make sure you remember to download it when it is complete.

8. For Subtitles we do not alter the existing encoding, so the size stays the same. If you need this MP4 for iOS devices, make sure the video size is correct before you submit because if iTunes needs to re-encode it to a different size, the subtitles may be dropped in the process.

9. On Windows, some players, like iTunes and QuickTime, need the file to have the .m4v extension to display the subtitles. So, after you download the encoded output, ensure you change the extension to .m4v, e.g., Bio_1.mp4 -> Bio_1.m4v .

10. For Open Captions we, by default, place the captions below the video and render a new file – this resultant file may have different quality characteristics than the original.

11. Open Captioning should be used as a last resort – when playback device constraints rule out traditional closed captioning. Open captioning takes control of the captioning away from the viewer – the text cannot be turned on or off, and the size of the text scales with the size of the playback screen (which can be problematic for mobile devices). Closed captioning (or subtitling) should be used whenever possible.

12. If you receive a Video Encoding Failure Message when requesting Open Captioning, follow the instructions in this article and try to repair the MP4, F4V, M4V, or MOV file. Then resubmit your file again.

13. The mp4 and m4v formats are essentially the same. The m4v file can contain Apple's FairPlay DRM, but not all m4v files must contain the DRM fields. When no DRM is present, the m4v file is essentially interchangeable with mp4. Indeed, you can just change the file extension by renaming it and the file will behave exactly as a mp4. However, some Apple products insist on a .m4v extension in order to play back the file; most other mp4 players will recognize the m4v extension. 
Our mp4 files have no FairPlay DRM -- so they are interchangeable with m4v files. This is why you can simply rename them to change the extension, if needed. We return them with the mp4 extension, but you can change them to m4v to ensure they are recognizable to Apple players (iPhone, iPad, AppleTV, etc).

You can learn more about the technical background on Video Encoding in this article. If you are experiencing playback issues with subtitles, please see this MP4/M4V Playback Issues article.