mp4 file changes size during playback
Mathieu Duponchelle
mathieu at centricular.com
Wed Dec 4 18:45:54 UTC 2019
I'm afraid I don't have these documents available to me anymore (pretty sure I got them at some point).
Perhaps someone else will read this and lend you their copy :)
On 12/4/19 7:03 PM, David Ing wrote:
> Mathieu --
>
> Please excuse the inadequacy of my google-fu. I am having trouble finding any kind of authoritative reference document which describes avc1, 2, 3, 4, ... (and the subtle differences between them)
>
> * My best guess is that avc1 refers to the first amendment:Â Â https://www.iso.org/standard/67318.html
> * My best guess is that avc3 refers to the third amendment:Â Â https://www.iso.org/standard/69728.html
>
> Also -- I am a bit surprised that we need to pay in order to view documents like this. Does anyone know if there is a way to view this stuff for free?
>
> On Wed, Dec 4, 2019 at 9:14 AM Mathieu Duponchelle <mathieu at centricular.com <mailto:mathieu at centricular.com>> wrote:
>
> That's an interesting file, but I'm not sure it is a a compliant one:Â the resolution change is
> advertised through SPS in the bitstream, but the MP4 header says "avc1", which as far as I remembe
> means the H264 bitstream should not contain any SPS (please double check this, haven't looked at the spec).
>
> Ideally, the tool you produced this file with would use an "avc3" stream format, and not hold
> any parameter sets in its MP4 header. That way, you could detect resolution changes by simply
> plugging a demuxer and a parser together and looking for new caps. Currently you can only do that
> either by also plugging a decoder afterwards and looking for caps changes, or analysing the SPS
> manually :)
>
> Best,
>
> --
> Mathieu Duponchelle · https://www.centricular.com
>
>
> On 12/3/19 10:50 PM, David Ing wrote:
>> I have an mp4 file which changes size during playback. But I noticed that gst-discoverer-1.0 does not report the fact that the size changes.
>>
>> I have two questions.
>>
>> 1. In theory, what is the fastest way to scan the file to determine where the size changes?
>> 2. In practice, what is the easiest way (given the current state of gstreamer) to scan the file and determine where the size changes?
>>
>> Here is the file which changes size during playback:
>>
>> https://drive.google.com/drive/folders/1f4pGNDhzCvsg1xXWj4y9DS3vXkaglOvZ?usp=sharing
>>
>> Here is the gst-discoverer-1.0 output:
>>
>> $ *gst-discoverer-1.0 -v screencap.m4v *
>> Analyzing file:///home/ding/mess/repro/screencap.m4v
>> Done discovering file:///home/ding/mess/repro/screencap.m4v
>>
>> Topology:
>> Â container: video/quicktime, variant=(string)iso
>> Â Â video: video/x-h264, stream-format=(string)avc, alignment=(string)au, level=(string)4.2, profile=(string)main, codec_data=(buffer)014d402affe1002b674d402a965402a835f35602d40404050000030001000003003ce060007d0000030177009a9503b4244d4001000468ce3520, width=(int)996, height=(int)632, pixel-aspect-ratio=(fraction)1/1, framerate=(fraction)30/1, interlace-mode=(string)progressive, chroma-format=(string)4:2:0, bit-depth-luma=(uint)8, bit-depth-chroma=(uint)8, parsed=(boolean)true
>> Â Â Â Tags:
>> Â Â Â Â video codec: H.264 / AVC
>> Â Â Â Â bitrate: 309812
>> Â Â Â Â datetime: 2019-11-01T17:40:33Z
>> Â Â Â Â title: n/a
>> Â Â Â Â container format: ISO MP4/M4A
>> Â Â Â
>> Â Â Â Codec:
>> Â Â Â Â video/x-h264, stream-format=(string)avc, alignment=(string)au, level=(string)4.2, profile=(string)main, codec_data=(buffer)014d402affe1002b674d402a965402a835f35602d40404050000030001000003003ce060007d0000030177009a9503b4244d4001000468ce3520, width=(int)996, height=(int)632, pixel-aspect-ratio=(fraction)1/1, framerate=(fraction)30/1, interlace-mode=(string)progressive, chroma-format=(string)4:2:0, bit-depth-luma=(uint)8, bit-depth-chroma=(uint)8, parsed=(boolean)true
>> Â Â Â Additional info:
>> Â Â Â Â None
>> Â Â Â Stream ID: 14c5bd3783191c8af25f30b00a879f8f7bdaa4367c8ecbd954b38e5367507175/001
>> Â Â Â Width: 1350
>> Â Â Â Height: 846
>> Â Â Â Depth: 24
>> Â Â Â Frame rate: 30/1
>> Â Â Â Pixel aspect ratio: 1/1
>> Â Â Â Interlaced: false
>> Â Â Â Bitrate: 309812
>> Â Â Â Max bitrate: 0
>>
>> Properties:
>> Â Duration: 0:00:34.861322222
>> Â Seekable: yes
>> Â Live: no
>> Â Tags:
>> Â Â Â video codec: H.264 / AVC
>> Â Â Â bitrate: 309812
>> Â Â Â datetime: 2019-11-01T17:40:33Z
>> Â Â Â title: n/a
>> Â Â Â container format: ISO MP4/M4A
>>
>>
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