[SOLVED] Remuxed mp4 forced to transcode

[YannMor]

This is (1) about an audio synchronization issue, which I think I resolved, and (2) about the PS3 not transparently streaming certain mp4 files as it should, and imposing transcoding on these files.

I have been streaming mp4 (x.264 AVC / ac3 audio) files for several years without any issue until I started processing TV recordings where I had to adjust the audio synchronization. I normally process my videos primarily with ffmpeg, and I found two issues:

(1) Regarding the video sync adjustment, many typical methods using ffmpeg or virtualdub seem to work as long as you test the result with players like VLC, Windows Media Player, Media Player Classic, etc., but the PS3 ignores these corrections. The only method I found was to demux the audio, apply the delay using beSweet, and remux it with the video (in the mp4 container). The process is very fast, and seems to work, but a new issue appears:

(2) Typically, my mp4 files are streamed by the PMS without any issue, and they are not transcoded, so that navigating inside the file, from 'chapter' to 'chapter' is very fast. However, the new mp4 files obtained by remultiplexing the audio and video streams via ffmpeg seem to require transcoding, and the video then plays slowly, with a stuttering effect, like one frame every 20 seconds (audio plays fine).
The only difference I can see between the mp4 that plays well without transcoding, and the one that doesn't, using MediaInfo, is that the first one seems to keep the encoding information, for example:

Code: Select all

Encoding settings                        : cabac=1 / ref=3 / deblock=1:0:0 / analyse=0x1:0x111 / me=hex / subme=7 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=0 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=6 / lookahead_threads=1 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=2 / keyint=250 / keyint_min=23 / scenecut=40 / intra_refresh=0 / rc_lookahead=40 / rc=crf / mbtree=1 / crf=21.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00

while the one that is transcoded has lost that information (as seen by MediaInfo).

Is there a workaround for that situation?
Thanks
Note: I'm using PMS 1.52.1 on XP, and a more recent version on Vista. Same behavior.
On the PS3, Information on the file not playing correctly (transcoding) shows MPEG-2, information on the file playing well (no transcoding) shows MPEG-4.

[YannMor]

Upon further investigation, it turns out that my BeSweet command was converting the ac3 audio into mp3. So, you do have to specify that the output should be ac3, same as the input. When I did that, the forced transcoding disappeared -- problem solved. Apparently, PS3 doesn't like mp3 audio in an mp4 container.