On 9/13/2023 6:34 AM, Tomas Härdin wrote:
ons 2023-09-06 klockan 16:16 -0300 skrev James Almer:
On 9/6/2023 2:53 PM, Tomas Härdin wrote:
ons 2023-09-06 klockan 11:38 -0300 skrev James Almer:
Signed-off-by: James Almer <jamr...@gmail.com>
---
This is an initial proof of concept for AVStream groups,
something
that's
needed for quite a few existing and upcoming formats that lavf
has no
way to
currently export. Said formats define a single video or audio
stream
composed
by merging several individualy multiplexed streams within a media
file.
This is the case of HEIF, a format defining a tiled image where
each
tile is a
separate image (either hevc, av1, etc) all of which need to be
decoded
individualy and then stitched together for presentation using
container level
information;
I remember this blocking HEIF as a GSoC project. Honestly the way
that
format is designed is immensely horrible.
MPEG-TS programs, currently exported as
AVProgram, which this new general purpose API would replace.
I can foresee this being a nuisance for users accustomed to
AVProgram.
Also this feature borders on NLE territory. Not necessarily a bad
thing, but FFmpeg is overall poorly architectured for NLE stuff. I
believe I raised this issue back when lavfi was proposed, it being
wholly unsuitable for NLE work.
+typedef struct AVStreamGroup {
+ /**
+ * A class for @ref avoptions. Set on stream creation.
+ */
+ const AVClass *av_class;
+
+ /**
+ * Group index in AVFormatContext.
+ */
+ int index;
+
+ /**
+ * Format-specific group ID.
+ * decoding: set by libavformat
+ * encoding: set by the user, replaced by libavformat if
left
unset
+ */
+ int id;
+
+ /**
+ * Codec parameters associated with this stream group.
Allocated
and freed
+ * by libavformat in avformat_new_stream_group() and
avformat_free_context()
+ * respectively.
+ *
+ * - demuxing: filled by libavformat on stream group
creation or
in
+ * avformat_find_stream_info()
+ * - muxing: filled by the caller before
avformat_write_header()
+ */
+ AVCodecParameters *codecpar;
+
+ void *priv_data;
+
+ /**
+ * Number of elements in AVStreamGroup.stream_index.
+ *
+ * Set by av_stream_group_add_stream() and
av_stream_group_new_stream(), must not
+ * be modified by any other code.
+ */
+ int nb_stream_indexes;
+
+ /**
+ * A list of indexes of streams in the group. New entries
are
created with
+ * av_stream_group_add_stream() and
av_stream_group_new_stream().
+ *
+ * - demuxing: entries are created by libavformat in
avformat_open_input().
+ * If AVFMTCTX_NOHEADER is set in ctx_flags,
then
new entries may also
+ * appear in av_read_frame().
+ * - muxing: entries are created by the user before
avformat_write_header().
+ *
+ * Freed by libavformat in avformat_free_context().
+ */
+ int *stream_index;
+} AVStreamGroup;
I see no provisions for attaching metadata, for example HEIF
stitching.
Putting it in coderpar seems wrong, since it is container-level
metadata. We could just have an HEIF specific struct as container
metadata.
The doxy for AVCodecParameters says "This struct describes the
properties of an encoded stream.", so It's not about container level
props.
It *is* container level props. The underlying codecs have no concept of
this kind of stitching. The closest you're going to get is tiles in
JPEG2000, but I doubt HEIF support JPEG2000.
We might say "well the resulting stream group has resolution so it's
like a codec" but see below.
Although codecpar will be used to export the merged/stitched stream
props like dimensions and channel layout, maybe you're right about
the
metadata because there would be a clash between actual
HEVC/Opus/AAC/AV1
extradata and the HEIF/IAMF/etc specific info if both use
codecpar.extradata, even if one will be in AVStream and the other in
AVStreamGroup.
Yes, pretty much. But it's more that codecpar is pressed into service
where it probably doesn't belong. It might be more appropriate to call
these "essence parameters". I'm going to stick my neck out further and
say that picture and sound essence should be handled with different
structs, not smushed together into one struct like AVCodecParameters.
Can you suggest how to approach this then, if not with
AVCodecParameters? For the resulting merged/stitched stream, we need at
the very least dimensions, and for audio we need channel layout, and for
each different kind of group type (HEIF, IAMF, TS programs) we need
specific parameters, like order of tiles for HEIF, mixing parameters for
IAMF, and these parameters should be in a form easy for the user (like
our CLI) to feed to lavfi, where the actual merging/stitching would take
place with new or existing filters for this specific purpose.
Maybe something like:
----
enum AVStreamGroupParamsType {
AV_STREAM_GROUP_PARAMS_NONE,
AV_STREAM_GROUP_PARAMS_TS,
AV_STREAM_GROUP_PARAMS_HEIF,
AV_STREAM_GROUP_PARAMS_IAMF,
};
typedef struct AVStreamGroupTSParams {
// Basically AVProgram
} AVStreamGroupTSParams;
typedef struct AVStreamGroupHEIFParams {
// dimensions, tile order, etc
} AVStreamGroupHEIFParams;
typedef struct AVStreamGroupIAMFParams {
// channel layout, mixing params
} AVStreamGroupIAMFParams;
typedef struct AVStreamGroup {
[...]
enum AVStreamGroupParamsType type;
union {
AVStreamGroupTSParams ts;
AVStreamGroupHEIFParams heif;
AVStreamGroupIAMFParams iamf;
} essence;
[...]
} AVStreamGroup;
----
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