Question

I’m trying to create a Mac App for internal use, that grabs a movie file specified by the user, converts it to a specific format and saves every frame as an image on the hard drive.
I’ve got the converting part done, using the awesome Handbrake CLI.

Now I’m trying to find a way to save each frame as an image, but I can’t find a way of doing it.

It seems ffmpeg has a command to extract frames into images. The following pulls a single frame five seconds in:

ffmpeg -i "infile.mp4" -r 1 -ss 00:00:05 -t 00:00:01 -vframes 1 -f image2 -y "image.jpg"

However, I’d rather use QTKit or the Handbrake CLI, so I won’t have to add both ffmpeg and Handbrake to the app.

Any ideas would be much appreciated!

Answer 1

So, I’ve found out for sure that you can’t do it with Handbrake, after a discussion on their IRC channel.

However, here’s a relatively painless way of doing it with ffmpeg:

NSNotificationCenter *defaultCenter = [NSNotificationCenter defaultCenter];
outputPipe = [NSPipe pipe];
taskOutput = [outputPipe fileHandleForReading];
current_task = [[NSTask alloc] init];

NSString *resourcePath = [[NSBundle mainBundle] resourcePath];

NSString *stillName = [NSString stringWithFormat:@"%@_still%d.png", [MY_FILE substringToIndex:([draggedFile length]-4)], MY_STILL_NUMBER];

[current_task setLaunchPath: [NSString stringWithFormat:@"%@/ffmpeg", resourcePath]];

// save just frame at current time
// by leaving -ss before the -i, we enable direct indexing within ffmpeg, which saves a still in about a second, rather than a minute or so on a long video file
NSArray *arguments = [NSArray arrayWithObjects:@"-ss", currentFrameTime, @"-i", draggedFile, @"-vframes", @"1", @"-f", @"image2", stillName, nil];

[current_task setArguments:arguments];
[current_task setStandardInput:[NSPipe pipe]];
[current_task setStandardOutput:outputPipe];
[current_task setStandardError:outputPipe];

[defaultCenter addObserver:self selector:@selector(saveTaskCompleted:) name:NSTaskDidTerminateNotification object:current_task];

[current_task launch];
[taskOutput readInBackgroundAndNotify];

So, i’m using a task for Handbrake (to convert video) and then another task to save a still.
I could use just ffmpeg, but I like Handbrake, so I’ll leverage the 2 this way.

Hope this helps anyone out there.