H.264 export choppy

[Ivan Myles]

I am unable to replicate the issue; the source clip looks fine at 24fps and the exported files did not have any repeated frames. Here is what I did in Premiere Pro CS6 (Win7-64):

1280×720-24fps Timeline

– Inserted the 1280×720-59.94fps source file on a 1280×720-24fps sequence with Speed/Duration set to 40%/850f.
– Imported another instance of the source file, used Interpret Footage to set frame rate to 24fps, and inserted a second clip onto the 1280×720-24fps sequence.
– Exported the 1280×720-24fps sequence to H.264, Level 4.1 Main, ABR 50, MBR 50, key frame interval 1 frame.
– The exported file plays fine in Windows Media Player. Playback was choppy in QuickTime 7.2, but that is a player issue (I could not find any repeated frames).
– Imported the 1280×720-24fps output file and inserted it onto the timeline; could not find any differences with the source clip.

1276×532-24fps Timeline

– Inserted the two source clips (one modified using Speed/Duration, the other using Interpret Footage) onto a 1276×532-24fps sequence as per your sample file.
– Exported the 1276×532-24fps sequence to H.264, Level 4.1 Main, ABR 50, MBR 50, key frame every 1 frame. No issues found with the exported file.
– Exported the 1276×532-24fps sequence to H.264, Level 4.1 Baseline, ABR 3, MBR 8, key frame every 72 frames. No issues found with the exported file.

When you look at the source clip on your 24fps timeline, are any of the frames repeated?

Are there any effects applied to the clip?

What are your export settings?

[Scott Talbot]

Before we go further, I really appreciate you helping me with this. I would be lost without your help.

This is definitely an exporting problem. I tried to follow the export settings you did but I’m wondering what ABR and MBR are. Are they the bitrates? Because I put them to 50 like you said and the file ends up being massive.

I exported with what you said but instead put 8 and 8 for the bitrates. I didn’t get the frame repeated anymore.

What do the bitrates mean? And what does the keyframe setting do? Because I think that was the fix. Also why would you render out at 50 BR and then import and render again at 8 and 3?

[Ivan Myles]

Good to hear you were able to resolve the issue. Here are the answers to your questions:

I’m wondering what ABR and MBR are.

ABR = Average Bitrate
MBR = Maximum Bitrate

What do the bitrates mean?

Bitrate is a measure of the amount of data used to store the file. In general, higher bitrates yield better quality, but require more file space and higher bandwidth. The ABR and MBR export settings tell the encoder how big you want the final file to be, and how much the data rate is allowed to vary.

Average bitrate is the total file size (megabits) divided by the length of the video (seconds). So a 60 second video that is 30MB in size (240 megabits) has an average bitrate of 4 megabits/second.

Bitrate can either be held constant or allowed to vary. In a variable bitrate (VBR) file, the maximum bitrate is the highest data rate at any point in the movie (typically during high motion scenes). Maximum bitrate is important when considering the amount of bandwidth required to play a video.

And what does the keyframe setting do?

Keyframes (aka I-frames) are reference frames that represent a full image of a video frame. Keyframes are similar to a jpg or png image of a picture. Typically, most of the frames in a movie are actually constructed of many small sections of the I-frames. This allows the file to be much smaller. However, more computing resources are required to encode each frame. Similarly, more processing power is required to reconstruct all the frames during playback, which is why video players sometimes skip. (The player takes too long to reconstruct each frame, so it has to leave out a few frames in order to play the movie at normal speed.)

Encoding with a keyframe distance to 1 makes it easier to view the output file but results in a larger file size. Increasing the keyframe distance will reduce file size, but more processing power is required to play the movie smoothly.

Also why would you render out at 50 BR and then import and render again at 8 and 3?

Those are two different settings for exporting the source file. The 50 ABR output file was not recompressed; the source file was saved twice at two different bitrate settings. My purpose was to test whether the problem was related to bitrate.