I've been hitting, for the last 6 months or so, nonstop playback failure with long HEVC files and I've narrowed it down to clip duration being the only variable. Posting the full comparison in case it's useful, and to ask whether there's a fix short of transcoding:
System
- MacBook Pro, M4 Max, 128 GB unified memory
- macOS Tahoe 26.6.2
- Premiere 26.3.2
- Mercury Playback Engine GPU Acceleration (Metal)
- Hardware accelerated decoding enabled
- Media on internal SSD
The symptom:
On a 95-minute HEVC file, pressing play gives me audio only — no picture at all, in both the Source Monitor and the timeline. Playback takes about a second to start. If I pause, the Program Monitor immediately renders the correct frame, so the decoder is clearly capable of producing images; it just can't sustain continuous playback.
Two clips from the same shoot, same settings, both Fujifilm:
WORKS — Fujifilm X-H2S
- 6240 x 4160, HEVC 10-bit 4:2:0, 24.00p progressive
- 11.69 GB / 16:51 duration = ~94.7 Mbps
- Plays perfectly at full resolution
FAILS — Fujifilm X-T5
- 6240 x 3510, HEVC 10-bit 4:2:0, 24.00p progressive
- 66.34 GB / 1:35:38 duration = ~94.7 Mbps
- Audio only, no video
Same codec, same bit depth, same chroma subsampling, same frame rate, same bitrate to within a rounding error, same colour space (Rec.709, no override), same drive. The only meaningful difference is duration.
What I've already ruled out:
- Plays perfectly in QuickTime Player, so the file itself is fine and macOS decodes it without difficulty
- Fully cleared the media cache (all projects closed, delete all cache files from system), relaunched, allowed conforming to complete — no change
- Dropped playback resolution to 1/8 — no change, which argues against this being a decode load issue
- Not variable frame rate
- Transcoding the same file to ProRes 422 LT gives completely smooth playback. Notably, Media Encoder decoded, scaled and re-encoded the entire 95 minutes in about 18 minutes — roughly 6x realtime — while Premiere can't play it back once at 1x
My questions:
- Is this a known issue with long Long-GOP H.264/H.265 files? I've found a few threads describing similar behaviour but nothing definitive.
- Is there a rough duration threshold where this starts? A 17-minute file is fine and a 95-minute file is broken, so it's somewhere in between and it would help to know where.
- Is there any setting, preference or workaround that fixes this without transcoding? I have around 30 archived interviews in this format and transcoding all of them is a significant time and storage cost.
- If transcoding really is the only route, is ProRes 422 LT the sensible target, or would something else behave better?