How to play and edit MPEG-2 files

I am preparing a Keynote presentation and need to use some pretty old footage. I have some material that I only have as .m2v files. I can view these in VLC (QT struggles) but can't edit them. I have MPEG Streamclip but it needs Quicktime MPEG-2 playback component to enable it to play these files - I believe that is long gone on my system and can't see how to re-install it (if I can).

If you still have the AppleMPEG2Codec.component installer package, then you should still be able to install the codec manually using the MPEG Streamclip installer utility, Pacifist, or the MacOS Finder. If the codec is currently installed on another system, then simply copy/move it from the source system to your current primary platform. While the codec is no longer available from Apple, it still works with legacy GUIs like QT 7 Pro and/or MPEG Streamclip.

Any advice on the best way to proceed?

1. If you still have/can reinstall the AppleMPEG2Codec.component then, in my opinion, the best workflow would be to convert the M2V or paired M2V/AIFF elementary file streams to an AppleProRes422/LPCM MOV file to both archive and edit the data retaining the highest level of quality available to the general user. Unfortunately the AVFoundation, Modernizer, Convert embedded structures are not programmed to properly transcode M2V or M2V/AIFF source content directly (even though they handle the individual codecs independently in the correct manner) and thus currently still requires a "legacy" app to properly re-mux the data to an MOV file container after conversion (M2V) and/or not locating the (AIFF) elementary stream file resource.
2. If you no longer have the codec installer package or a copy of the codec, then you could try using HandBrake to convert the M2V video to H.264 video which is fully playback, edit, and conversion compatible with any Apple app. Unfortunately, this workflow may retain less visually quality and will either lose the audio (if the elementary stream resource was included in paired source files) and will probably "hang up" after the video conversion has completed, forcing you to manually terminate the transcode process (once the progress bar has reached 100%).

NOTE: Above workflows were tested using MacOS v10.12.5 this morning and confirmed to still work.

I did buy AppleMPEG2Codec.component way back but I can no longer find it on my system and can't see anywhere to download it again.

Apple stopped providing "permanent" backup downloads several years ago before they stopped selling this product. If you did not download and maintain a copy within the time allotted, then Apple purged the file from your account years ago.

As you say, it might not run on Sierra anyway.

I repeat, I tested the "legacy" QT 7 Pro and MPEG Streamclip workflows this morning under the latest Sierra update (MacOS v1012.5)—it still works and remains the best option if you wish to retain maximum video quality.

For some reason QT Player 7 won't open the .m2v file (maybe because of the missing component?)

Correct! All legacy apps require the purchased codec for "open" architecture use. QT X has a different playback codec installed for its own "passive" use.

but I am now trying to convert it to a .mov file in the regular QT Player - that will open the file but won't play it.

Strange! What MacOS are you using? Both M2V video only and M2V/AIFF elementary stream files open and play the video on my system in the QT X player but the QT X player (AVFoundation) does not support audio track playback of a resource in a separate file or the playback of M2V/AIFF in a single MOV file container. (I.e., I suspect programmers never consider the use of such files and neglected to program the QT X GUI or the embedded structures to handle them.)

On this occasion audio is not an issue so I would be happy to just get a good quality conversion of the video footage.

Then HandBrake (free) or any third-party converter based on the FFmpegX codec package should work here. Just remember that HandBrake will likely "hang" after converting the video and you will likely have to manually terminate conversion manually to write the EoF (End of File) and get the Finder to recognize the "finished" file.

I did convert to H264 in VLC but that seemed unstable when I opened it in my editing software (Avid Media Composer).

This frequently happens and is why I always recommend use of HandBrake instead.

The QT conversion has now completed but unfortunately has only converted the middle section of the video - the start and end are black. Strange.

Did you merge more multiple M2V segments? If so, that may explain the problem. "Legacy" apps support up to 99 independent data tracks composited in layers and/or display areas. Modern apps like QT X and HandBrake expect AV data "flattened" to a single audio and a single video track converted MPEG4 or AVC output.

I am now trying Handbrake but the conversion file types are limited.

Any of the presets targeting H.264 or MPEG4 video equal to or greater than your source resolution should work for test purposes. (You can manually adjust quality, anamorphic, and "tuning" settings once you are satisfied with basic the workflow.) Just remember that the conversion will likely hang once the video is converted and you may have to manually terminate conversion.

I can't remember how this file was created but its a single .m2v file

M2V files are normally created when demuxing or importing "muxed" MPEG2 content or exporting classic FCP files for burning to optical media. In any case, it doesn't seem to matter on my system whether the M2V only contains a single video track or a self-contained video track along with AIFF audio track pointing to a secondary audio file that contains the actual audio data. Both types of M2V files convert the same on my system.

The conversion did seem to complete - at least it said it had - the file wouldn't play in QT X but seemed fine in VLC and QT 7. I am now trying to import it into Media Composer to see if I can work with it.

Once again, "What MacOS are you using?" This may or may not account for playback differences. VLC uses its own built-in playback support. QT X uses the AVFoundation for playback. And QT 7 uses the "classic" QT embed that specifically supports "legacy" playback. The only question at this point is whether Media Composer is based on a "modern" or "legacy" support structure. If the file opens and is edit compatible with the editor and you are satisfied with the results, then you have a solution. If not, then I would probably recommend seeking an alternative solution. For instance, in addition to the QT 7 Pro and MPEG Streamclip ProRes422 (MOV) conversions previously described, I have since managed to also use iSkysoft iMedia Converter Deluxe (third-party purchase) to create a ProRes422 MOV file. I really like the ProRes422 solution because the file is AVFoundation supported making it fully compatible with QT X natively. The only thing that might be a problem for some users is the fact that ProRes422 files are much larger than source M2V files since they're specifically used for archiving and editing data before recompressing the final project for distribution or a particular targeted use.

MPEG StreamClip with the QuickTime component would have been a good way to do this but I do not believe this is possible to do under Sierra - it was with some effort in Yosemite.

It maybe that you will first need to convert the MPEG2 recording to a better supported format i.e. MPEG4. Then you will have a much bigger choice of MPEG4 editors you can use including MPEG StreamClip.

In terms of converters opening the MPEG2 recording in QuickTime Player and saving it might be one approach, or using Handbrake. See https://handbrake.fr/

VLC is supposed to be able to convert files but I find it in general completely hopeless, I would only use it as a player. Yes the normal QT Player will not open it, it should instead immediately say it needs to convert it. I have not tried this recently with QT Player as these days I use Handbrake.