MXF/MPG broadcast format support: handle multichannel audio properly

Problem: MXF and MPG files (TV broadcast formats) often contain:
- Multiple audio streams (4-8 streams for different language tracks)
- Multichannel layouts (5.1, 7.1) instead of stereo
- Default ffmpeg behavior was -c:a aac without channel limit, which
  meant multichannel got transcoded as multichannel AAC, overwriting
  what should have been clean stereo

Solution:

1. get_audio_streams() helper probes all audio streams with ffprobe
   - Returns codec, channels, sample_rate, language, layout for each

2. build_audio_args() picks best stream + downmix:
   - Prefers first 2-channel stereo stream (usually main mix)
   - Falls back to first stream if none are 2-ch
   - Always: -ac 2 (force stereo downmix), -ar 48000, -c:a aac, -b:a 192k
   - Bitrate raised from 128k to 192k for music quality

3. Smart trim path now detects broadcast formats:
   - .mxf, .mpg, .mpeg, .ts, .m2ts, .mts → transcode (not stream copy)
   - Standard MP4/MOV → stream copy (faster, lossless)

4. Pre-conversion step for broadcast files without trim:
   - Even without --start/--duration, MXF/MPG get converted to MP4
   - Same audio handling as trim path

5. Main render adds explicit -map 0:v:0 -map 0:a:0? -ac 2 to ensure
   only first video and first audio stream get encoded, with stereo

6. ACR recognize also gets -map 0:a:0 -ac 2 for MXF compatibility

7. UI accepts: video/*,.mxf,.mpg,.mpeg,.ts,.m2ts,.mts

8. Upload limit raised: 2GB → 10GB (MXF files are large)

This means a TV broadcast MXF with [SLO/EN/DE language tracks] now
correctly outputs stereo MP4 with the main language track preserved.

This commit is contained in:

sebastjan

2026-04-29 14:38:48 +00:00

parent b543057cee

commit 1cc8e8be35

3 changed files with 126 additions and 9 deletions

									
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				          </svg>

				          <div>Klikni ali povleci video sem</div>

				          <div class="small">.mp4, .mov, .webm — do 2 GB</div>

				          <input type="file" id="file-input" accept="video/*" style="display:none">

				          <input type="file" id="file-input" accept="video/*,.mxf,.mpg,.mpeg,.ts,.m2ts,.mts" style="display:none">

				        </div>

				      </div>